add cbmonitor.sc.couchbase.com to allowed hosts

Change-Id: I1534580a49e7c465b2f8298aabac8a021880d6db
Reviewed-on: http://review.couchbase.org/31060
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>