PYCBC-125: Provide connection-object lock (threading) options

Change-Id: I8e7274da52b9d8b9a06f875a200db3ad13dd53f8
Reviewed-on: http://review.couchbase.org/26769
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Reviewed-by: Rami Chowdhury <rami@esplorio.com>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>