Remove distribute dependency

Direct depends on distribute are evil and can break python on entire
systems in certain combinations.

Change-Id: If96e415e5395f3cbc1babae0fe95b52dc51e5176
Use the python in the virtualenv for everything

Upgrade the tox requirements to match the rest of OpenStack. Benefits
include not making an sdist first, and ensuring that the virtualenv is
use for all actions.

Change-Id: Ib0b135e096de0c4ab02278be94898867265c90f9