Deactivate dashboard plugin until fixed
Deactivate dashboard plugin until fixed

I deactivated the watcher-dashboard plugin in the docs since it
doesn't at the moment. Will be reactivated once it gets fixed
(see https://bugs.launchpad.net/devstack/+bug/1540328).

Change-Id: I65de8ca4a08cdb294d0e48eac52927eed13ec66c

stackforge/watcher,openstack/watcher,stackforge/watcher,openstack/watcher