According to Openstack summit session ,
stestr is maintained project to which all Openstack projects should migrate.
Let's switch to stestr as other projects have already moved to it.
Sphinx 1.5 fails with current pbr (needs new pbr release, see change
For now, set warnerrors to False to be able to use this.
Also, update to new sphinx version to show that this works.
This is in reaction to the failure in