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: I81f93eb693a4c0e0527d2a9ab99790e516da97a8