Update minversion of tox to 3.9.0 to allow inline comments.
Add skipsdist and ignore_basepython_conflict for better compatibility
and to use correct python version when specified.
Move pep8 test requirements to tox.ini for easier management and update
requirement versions.
Fix a small typo found with new pep8 deps.
Add py27 constraints file for Python 2.7 tox jobs.
Use wallaby jobs.
Remove lower-constraints (it was not used anyway).
Fix docs job
Change-Id: I1132814a86b46a154b3a8eed5bc3e73ad7950589
