MB-10640: Start the snapshot with a marker

There is an UPR protocol change. Not the snapshot marker is no
longer at the end of a snapshot, but at the beginning.

Change-Id: I930163663d9027b23dfa8527a6ccdb509b92a236
Reviewed-on: http://review.couchbase.org/35902
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Tested-by: Volker Mische <volker.mische@gmail.com>