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: Ic0ddaae3bd0a4ad4e34264429f717a292e17a1c9
Signed-off-by: Charles Short <zulcss@gmail.com>