Set up for publishing via openstack-doc-tools

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

tox -e publishdocs-api is the job for api.openstack.org.

Additionally, remove parameter --api-docs from
openstack-doc-tools invocation, it is set in doc-test.conf now.

Change-Id: I84986e1572d128b85ad43863217e4d6c0b22f41f
Merge "Set up for publishing via openstack-doc-tools"