Propose black py27 + py35 mode for the rest of Py2K

Propose black py27 + py35 mode for the rest of Py2K

py27 mode produces one failure for flake8 which is the
space added between exec and parenthesis.  however apparently
we can add multiple versions to target-versions which allows
the exec() calls to come out in python 3 style.

The issue we want to improve is issues of trailing
commas being added.  I'm not really able to get black to
consistently add or remove these trailing commas in any
case no matter what I set target-version towards.

Change-Id: Iceb9e9aeb5f5e0d317fb877ef06eca0290997fe4
(cherry picked from commit 5850dbca071a565cc00f613618b4fcddd13a5eee)