Start adding a environment for py34/py33

Get a tox environment for py34/py33 that doesn't stop the existing
py26 and py27 to continue working with the adjusted test-requirements since
MySQL-python and sqlalchemy-migrate do not yet exist in 3.x.

Note that this does not fully make py34 work yet but it starts to work
in this direction of getting it to work (which will apparently require
quite a big more tweaking).

Change-Id: I024957a76f2de0bd406d14da5af6e4caf3d493e7
Merge "Start adding a environment for py34/py33"