Set up for publishing via openstack-doc-tools

tox -e publishdocs will be called by the post jenkins jobs to prepare
everything for publishing - and then the content of publish-docs
gets copied.

Additionally, remove some parameter from openstack-doc-tools invocation,
they are now set in doc-test.conf.

Change-Id: I5966dfb1bbfa85a92b19eabc438218ea7d7b15cf