Fix up a variety of Python version issues.

Review Request #9880 — Created April 19, 2018 and submitted — Latest diff uploaded

Information

RBTools
release-1.0.x
30c0d1f...

Reviewers

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.