PYCBC-96: Expose lcb errors

Change-Id: I545791f36ef0478063ae3df7594d2b89e4990a20
Reviewed-on: http://review.couchbase.org/25995
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Mordechai Nunberg <mnunberg@haskalah.org>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>