PYCBC-95: Don't require username/passwords

Change-Id: I3c4becf61c3419eb96763fb9419ceb794a5e6b9f
Reviewed-on: http://review.couchbase.org/25993
Reviewed-by: Mordechai Nunberg <mnunberg@haskalah.org>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>