With the latests changes to os-testr[0] it now expects
a .stestr.conf file instead of a .testr.conf file. This
change migrates the testing suite from using testr to
use stestr instead.
[0] http://lists.openstack.org/pipermail/openstack-dev/2017-September/122135.html
Change-Id: Ie0de862f2192491fa7752af03c8c03b3ee36337a
Gage Hugo