This repo is now testing only with Python 3, so let's make
a few cleanups:
- Remove python 2.7 stanza from setup.py
- Add requires on python >= 3.6 to setup.cfg so that pypi and pip
know about the requirement
- Remove obsolete sections from setup.cfg
- Update classifiers
- Use newer openstackdocstheme and Sphinx versions
- Cleanup */source/conf.py to remove now obsolete content.
- Remove Babel from requirements, it's not needed for running.
- Sync docs deps in tox.ini
Change-Id: Ie1fccdc777be978075e4689eda6c62578bd463e4
02b82e5a4c