Fix Tox

We can now run the tests using the `tox` command without needing to have the
Horizon source checked out alongside (the horizon package is a test dependency).

All tests except for Django 1.4 are currently passing.

Change-Id: Id835e14868225a7bc13ff25bc666547a85d085e5
Signed-off-by: Tomas Sedovic <tsedovic@redhat.com>
Merge "Fix Tox"