Update changes.
Update Rackspace loadbalancer driver to use 'datacenter' kwarg.
Update affected Rackspace LB tests.
Add unittest2 dependency for tests and use it if Python version is not in
['2.7', '3.x'].

Also update some of the affected tests to use unittest2.
Update changes.
Add a better comment.
Merge branch 'trunk' into make_rackspace_drivers_multi_datacenter_aware
Fix broken fixture.