COMPAT: Add Google BigQuery support for python 3 #11094
closes #11094 

Adds gbq support for python 3.4 

Python 3.5 unit tests are failing, waiting on #11097
See https://travis-ci.org/parthea/pandas/builds/80424117
 @parthea yes, 3.5 are ok
 Some gbq unit tests are failing on Python 3.4 

I think I need to remove the `bq` command line module from `test_gbq.py`, as it doesn't support python 3. I'm going to create a new PR for adding ability to create and delete datasets using `create_dataset()` and `delete_dataset()` and at the same time remove the `bq` command line tool.

```
ERROR: Python 3 is not supported by the Google Cloud SDK.  Please use a Python 2.x version that is 2.6 or greater.

If you have a compatible Python interpreter installed, you can use it by setting the CLOUDSDK_PYTHON environment variable to point to it.
ERROR: Python 3 is not supported by the Google Cloud SDK.  Please use a Python 2.x version that is 2.6 or greater.

If you have a compatible Python interpreter installed, you can use it by setting the CLOUDSDK_PYTHON environment variable to point to it.
test_upload_data_if_table_exists_replace (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ERROR
ERROR: Python 3 is not supported by the Google Cloud SDK.  Please use a Python 2.x version that is 2.6 or greater.

If you have a compatible Python interpreter installed, you can use it by setting the CLOUDSDK_PYTHON environment variable to point to it.
```
 @parthea gr8. let me know when ready for review.
 whatsnew note as well.
 add a whatsnew entry (in the gbq sub-section that you did before).
 Can I wait for #11121 to be merged?
 ok, rebase this, ping when green.
 @aaront @parthea can you update this?
 @aaront You are welcome to work on this if you have time, but don't feel obligated. I plan to commit a new version tomorrow evening.
 @parthea @jreback Yeah, I'll rebase and run the tests.
 @parthea @jreback  Rebased & ran tests in 3.4, 3.5, and 2.7. All passing.
 Travis is green
 can you certify that all tests are passing on py2 and py3? (as we skip the actual tests on travis).
 Ready for review. All tests pass locally.

Python 2.7 test results

```
nosetests test_gbq.py -v
test_should_be_able_to_get_a_bigquery_service (pandas.io.tests.test_gbq.TestGBQConnectorIntegration) ... ok
test_should_be_able_to_get_results_from_query (pandas.io.tests.test_gbq.TestGBQConnectorIntegration) ... ok
test_should_be_able_to_get_schema_from_query (pandas.io.tests.test_gbq.TestGBQConnectorIntegration) ... ok
test_should_be_able_to_get_valid_credentials (pandas.io.tests.test_gbq.TestGBQConnectorIntegration) ... ok
test_should_be_able_to_make_a_connector (pandas.io.tests.test_gbq.TestGBQConnectorIntegration) ... ok
test_bad_project_id (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_bad_table_name (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_column_order (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_column_order_plus_index (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_download_dataset_larger_than_200k_rows (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_index_column (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_malformed_query (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_arbitrary_timestamp (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_empty_strings (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_false_boolean (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_null_boolean (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_null_floats (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_null_integers (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_null_strings (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_null_timestamp (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_timestamp_unix_epoch (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_true_boolean (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_valid_floats (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_valid_integers (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_valid_strings (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_unicode_string_conversion_and_normalization (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_zero_rows (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_read_gbq_with_no_project_id_given_should_fail (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_should_return_bigquery_booleans_as_python_booleans (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_should_return_bigquery_floats_as_python_floats (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_should_return_bigquery_integers_as_python_floats (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_should_return_bigquery_strings_as_python_strings (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_should_return_bigquery_timestamps_as_numpy_datetime (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_that_parse_data_works_properly (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_to_gbq_should_fail_if_invalid_table_name_passed (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_to_gbq_with_no_project_id_given_should_fail (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_create_dataset (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_create_table (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_dataset_does_not_exist (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_dataset_exists (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_delete_dataset (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_delete_table (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_generate_schema (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_google_upload_errors_should_raise_exception (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_list_dataset (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_list_table (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_list_table_zero_results (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_table_does_not_exist (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_upload_data (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_upload_data_if_table_exists_append (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_upload_data_if_table_exists_fail (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_upload_data_if_table_exists_replace (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
pandas.io.tests.test_gbq.test_requirements ... ok
pandas.io.tests.test_gbq.test_generate_bq_schema_deprecated ... ok

----------------------------------------------------------------------
Ran 54 tests in 346.397s

OK
```

Python 3.4 test results

```
nosetests test_gbq.py -v
test_should_be_able_to_get_a_bigquery_service (pandas.io.tests.test_gbq.TestGBQConnectorIntegration) ... ok
test_should_be_able_to_get_results_from_query (pandas.io.tests.test_gbq.TestGBQConnectorIntegration) ... ok
test_should_be_able_to_get_schema_from_query (pandas.io.tests.test_gbq.TestGBQConnectorIntegration) ... ok
test_should_be_able_to_get_valid_credentials (pandas.io.tests.test_gbq.TestGBQConnectorIntegration) ... ok
test_should_be_able_to_make_a_connector (pandas.io.tests.test_gbq.TestGBQConnectorIntegration) ... ok
test_bad_project_id (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_bad_table_name (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_column_order (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_column_order_plus_index (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_download_dataset_larger_than_200k_rows (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_index_column (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_malformed_query (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_arbitrary_timestamp (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_empty_strings (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_false_boolean (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_null_boolean (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_null_floats (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_null_integers (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_null_strings (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_null_timestamp (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_timestamp_unix_epoch (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_true_boolean (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_valid_floats (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_valid_integers (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_should_properly_handle_valid_strings (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_unicode_string_conversion_and_normalization (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_zero_rows (pandas.io.tests.test_gbq.TestReadGBQIntegration) ... ok
test_read_gbq_with_no_project_id_given_should_fail (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_should_return_bigquery_booleans_as_python_booleans (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_should_return_bigquery_floats_as_python_floats (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_should_return_bigquery_integers_as_python_floats (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_should_return_bigquery_strings_as_python_strings (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_should_return_bigquery_timestamps_as_numpy_datetime (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_that_parse_data_works_properly (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_to_gbq_should_fail_if_invalid_table_name_passed (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_to_gbq_with_no_project_id_given_should_fail (pandas.io.tests.test_gbq.TestReadGBQUnitTests) ... ok
test_create_dataset (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_create_table (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_dataset_does_not_exist (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_dataset_exists (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_delete_dataset (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_delete_table (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_generate_schema (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_google_upload_errors_should_raise_exception (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_list_dataset (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_list_table (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_list_table_zero_results (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_table_does_not_exist (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_upload_data (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_upload_data_if_table_exists_append (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_upload_data_if_table_exists_fail (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
test_upload_data_if_table_exists_replace (pandas.io.tests.test_gbq.TestToGBQIntegration) ... ok
pandas.io.tests.test_gbq.test_requirements ... ok
pandas.io.tests.test_gbq.test_generate_bq_schema_deprecated ... ok

----------------------------------------------------------------------
Ran 54 tests in 346.396s
```
 thanks @parthea @aaront 
