Thorough replacement of git.openstack.org URLs with their opendev.org counterparts.
The contributing.rst file was referencing a non-existing path, and
index.rst referenced a non-existing usage.rst file.
Added build-openstack-sphinx-docs job to test doc changes
This tempest plugin is being split out of the main mistral project in
accordance with Queens goal "Split Tempest Plugins into Separate
Repos/Projects". This patch applies the standard boilerplate files
for OpenStack projects so that it can stand on its own.