Since the horizon remove the 'run_tests.sh' file,
so there should remove '.venv' from the '.gitignore' file.
See the patch 'https://review.openstack.org/#/c/399842/'
Change-Id: I0ab7530aff41877914c3d1e3368baf98d200a721
Freezer Dashboard now support the latest version of freezer api.
Minor update in tox.ini to disable old style classes warnings
Change-Id: I6549a7587be1a39fbed280de5543125cfeb16807