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: Ifb460199c94d748988d4f0e836e90d1dd6f294bc
Signed-off-by: Chuck Short <chucks@redhat.com>