PYCBC-142: Clarify usage of the 'port' parameter

Change-Id: If13762c357d1612185c1276185c3f80e03db38c5
Reviewed-on: http://review.couchbase.org/27084
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>