cbvdiff to find VBs where active != replica

Change-Id: Idd5a43170bac61cc15ee1ed80a68b515b88b778c
Reviewed-on: http://review.couchbase.org/38029
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Tested-by: Sundararaman Sridharan <sundar@couchbase.com>