Make a few cleanups:
- Remove obsolete sections from setup.cfg
- Remove install_command from tox.ini, the default
is fine
- Switch to sphinx-build
- Enable warnings for doc build, fix all warnings
- Remove git handling from conf.py, openstackdocstheme does this now
- Cleanup tox.ini
Change-Id: I51796be20596afc2305c2d8ea189b4037bd28b2d
7f2b19452f