Some docs used external links which cannot be verified and thus we
easily might get broken links. Use internal links that Sphinx can verify.
Some additional updates:
* Update tox.ini to not publish the dirtrees.
* Update openstack mailing list to openstack-discuss
* Remove reference to not anymore existing 'OpenStack Configuration
Reference'
Change-Id: I9a613fa682021fab7bbaba90b219adaa7d9384d3