Remove KEYSTONE_CATALOG_BACKEND from DevStack plugin
Remove KEYSTONE_CATALOG_BACKEND from DevStack plugin

Via Sean Dague in the mailing list:
In Newton, the KEYSTONE_CATALOG_BACKEND variable will be removed.
This commit removes the if check and variable from watcher

Change-Id: I73c5dd25feff9ba9824c267a8817a49e4ad3a06a
Closes-Bug: #1544433

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