Create Commons role to provide a ForeignDBViaLBRepo wiki

Provision a wiki at http://commons.wiki.local.wmftest.net/ and setup
a ForeignDBViaLBRepo connection to it from the main wiki. Images for commons
are stored in /srv/commonsimages.

Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/632
Change-Id: I9ad7b25ae55195e413357ba50421f492d97dc0b5