We can now use PyMySQL in py3.x tests

The requirement for PyMySQL got merged into the requirements
repo, so now instead of just testing sqlite (or postgres) in py3.x
we can now test against the mysql instance that should exist in the
test environments (just like we test with MySQL-python in py2.x).

Change-Id: I6e48df78d20389d65de8210c6157abb99f52d7dd
Merge "We can now use PyMySQL in py3.x tests"