Since manila is now an incubated project, use oslosphinx together with
the incubated theme.
Unset html_static_path since there's currently no static file and sphinx
warns otherwise.
Change-Id: Icfbf2c0ee214da870c3c711a34b6a649e9878659
Remove intersphinx from the docs build as it triggers network calls that
occasionally fail, and we don't really use intersphinx (links other
sphinx documents out on the internet)
This also removes the requirement for internet access during docs build.
This can cause docs jobs to fail if the project errors out on
warnings.
Change-Id: I71e941e2a639641a662a163c682eb86d51de42fb
Closes-Bug: #1368910
