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: I847368004d14c2f213d36c602398abfdbfa381cd
Signed-off-by: Charles Short <zulcss@gmail.com>