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: I7eaadde83243afed1929bd29fff63272e58e072b
See https://review.openstack.org/283511 for history.
Change-Id: I7733e8786d6b525a7c9a8d4f12add329cd030d9d
Partially-Implements: blueprint designate-tempest-plugin