precursor to Split out test_pytables.py to sub-module of tests
- precursor to #18498
- All tests in test_pytables are passing
@simonjayhawkins as discussed this is the pre work to splitting this large test file into smaller files. So far, I have fixturised the class base class and updated methods using self.path from base to use the setup_path fixture instead.

Next I plan to create a test file for TestTimezones class and make the test functional so the class itself is no longer required.
Once this is running fine, I will then apply similar approach to the other bigger classes.
Hello @tolaa001! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2019-10-01 13:14:18 UTC thanks @tolaa001 for the PR!

just to be clear, there is a non-trivial amount of effort for #18498 and will require several PRs.

this PR is to add a couple of fixtures in order to eliminate the Base class. In this PR, the fixtures replicate the current unittest setup and teardown methods only and improving these fixtures and adding additional fixtures for some of the assertions will come later.

the next PR would be to split on complete classes. There are 3 test classes in `pandas/tests/io/pytables/test_pytables.py`, `TestHDFStore`, `TestHDFComplexValues` and `TestTimezones`.

so the first split would split `TestHDFComplexValues` and `TestTimezones` from test_pytables.py into test_complex.py and test_timezones.py (and move the two fixtures created here to a conftest.py) but this would need to be a seperate PR with code moved and miniamal code changes to make the diff simpler to review.

This PR is preparing for that split.

`TestHDFStore` could then be split further once the classes have been separated.
 > next steps would be to move test_pytables to a sub-dir

already a sub-dir so no need to nest further.