MB-11114: Set snapshot_start_seqno and snapshot_end_seqno

UPR protocol requires to set these fields when starting a session.

Change-Id: Ic342676af4938d431f5bf94ad25aff36c98f0ed3
Reviewed-on: http://review.couchbase.org/37097
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Reviewed-by: Steve Yen <steve.yen@gmail.com>
Tested-by: Bin Cui <bin.cui@gmail.com>