The 'openstack-tox-docs' gate is currently broken:
`html_static_path entry '_static' does not exist`
Removed the 'html_static_path' from 'doc/source/conf.py' as this is
also how Tempest is configured [0]
[0] https://github.com/openstack/tempest/blob/master/doc/source/conf.py#L125
Change-Id: I1244457428cbefb9341a1991839d41b592b6c469