introduced cluster compat mode for Sherlock release

Change-Id: I6e74dec05a9ca753cf558861667a9c24651bb071
Reviewed-on: http://review.couchbase.org/42867
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>