Test pytables refactor
 - precursor to #18498 and continuation of #28715
- No new tests added
- black pandas ran successfully
- This PR is the next step reference in #28715. 

@simonjayhawkins and @jreback as promised, this PR contains the following new and EXCITING changes:

1. Created a contest.py in the pytables sub directory containing all the shared fixtures
2. Created common.py which contains all the functions and variables used by the test classes such as tables, safe_remove, safe_close, create_tempfile, ensure_clean_path, ensure_clean_store, _maybe_remove
3. Created separate modules for each of the test classes i.e. test_timezones, test_hdf_store, test_hdf_complex_values
4. As a result of creating the common.py, I have update the ensure_clean_path import to the test_compat module to ensure safe deletion of the test_pytables module.

There has been no amendments to the body of the code. The next PR will involve focusing on removing the class in test_timezone and making it strictly functional. Followed by me doing this to the other 2 new modules i.e. test_hdf_store and test_hdf_complex_values.

Once the code base is strictly functional, I can start working on more fun refactoring of the functions :)
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 2019-10-04 10:09:29 UTC @tolaa001 you have some failing checks, if you can fixup we should merge this soon to prevent conflicts. > @tolaa001 you have some failing checks, if you can fixup we should merge this soon to prevent conflicts.

@jreback all green now and reverted my accidental changes to test_operators.py. Thank you again for reviewing this thanks @tolaa001 very nice.

love to have the followups as discussed above.