Updated openstack/openstack
Project: openstack/cinder  276d7ab650c73c98ffd81cddca5e7d61a4780841

Add specific docs build option to tox

Now the documentation can be build in a clean virtual env with "tox
-edocs".

Change-Id: I0f2752f200caa21ad0f26e53df5c2757dd94c78a