We had this library capped at a release that is a few years old. Now
that we have dropped py2 testing, we can pick up the latest version.
This uncovered a few things to clean up. Mostly the fact that mock is
now a part of the StdLib unittest since Python 3.3.
Change-Id: I27484dd4c25378413ff16e97a35a1a46062357bc
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>