MB-10151: fixed tunable Memory UI

Change-Id: I81a3875c2f8cedff6fff59c6686d8bbe051fc192
Reviewed-on: http://review.couchbase.org/33793
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>