Fix up a variety of Python version issues.
Review Request #9880 — Created April 19, 2018 and submitted — Latest diff uploaded
This change updates our Python version requirements, enabling 3.5+,
getting rid of 2.6, and removing a bunch of workarounds for old
versions.Based on work by Joshua Olson at https://reviews.reviewboard.org/r/9652/
- Ran unit tests on Python 2.7 and 3.6.
- Posted some changes.