PYCBC-221: txcouchbase and gcouchbase are no longer experimental

Change-Id: Iec1d6e34ae4d1b3234cc2f3b3b408baac1088d28
Reviewed-on: http://review.couchbase.org/35692
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>