MB-27231: Add cluster compat version APIs for 5.1
MB-27231: Add cluster compat version APIs for 5.1

Change-Id: I96d9b8a70b3873cad9599544fdbb48132e4554b6
Reviewed-on: http://review.couchbase.org/87059
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Tested-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>

membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server