TST: Add unit tests for older timezone issues
- [x] closes #8616
- [x] closes #8910
- [x] closes #7825
- [x] closes #8306
- [x] closes #8531
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

In the spirit of your https://github.com/pandas-dev/pandas/pull/21407#issuecomment-396896678 @jreback, cleaned up some old timezone issues (but not necessarily covered by #21407) that appear to have been solved