Transition notifier stream state to dead when ending the stream

Previously we would wait until sending the end stream message to
transition to dead state. This caused problems because if multiple
notifications for a seqno happen before we actually send the end
stream message then we might schedule the end stream message to be
sent twice.

Change-Id: I0dfc929a967b896673c8bace8b3eda1251b95997
Reviewed-on: http://review.couchbase.org/35212
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>