According to Openstack summit session [1],
stestr is maintained project to which all Openstack projects should
migrate.
Let's switch to stestr as other projects have already moved to it.
[1] https://etherpad.openstack.org/p/YVR-python-pti
Change-Id: Ia64e4e4e44bc8ce7a86b471b0e60599fb285699f
Eric Fried