PYCBC-195: persist_to/replicate_to for delete

Change-Id: I648c346ed32df8e4a7d0b9084dcc0b80ba04b41a
Reviewed-on: http://review.couchbase.org/29691
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Volker Mische <volker.mische@gmail.com>