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
NOTE(tonyb): We set the minimum acceptable version of stestr to
>= 1.0.0 to align with trhe current value in stable
Change-Id: I55060b1d99b9a00b20c98fbb429d072568265695
(cherry picked from commit 32a3244bb4)