PYCBC-192: Propagate lockmode

Change-Id: I60c1f72aa5acf6ba07cff6e673f634cc93c182ba
Reviewed-on: http://review.couchbase.org/29261
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>