Since the horizon remove the 'run_tests.sh' file,
so there should remove '.venv' from the '.gitignore' file.
Change-Id: Iccddfef8e2733c0a2440ad940e6de674ec538b37
According to Openstack summit session [1],
stestr is maintained project to which all Openstack projects should migrate.
So we should switch to stestr.
[1] https://etherpad.openstack.org/p/YVR-python-pti
Change-Id: Iee13deb54056e1c81d3732cb51a61c68481607fa