According to Openstack summit session [1] stestr is
maintained project to which all Openstack projects
should migrate. Let's switch it then.
[1] https://etherpad.openstack.org/p/YVR-python-pti
Change-Id: Id31d458418d904b568be0adf98d5b579cfd841cd
Signed-off-by: Charles Short <zulcss@gmail.com>