MB-19673: Log the actual last seqno sent before closing the stream.

MB-19673: Log the actual last seqno sent before closing the stream.

(Note: backport of MB-19627 to 3.0.x)

When a DCP stream closes, we log the last sent seqno at the time when
stream transitions to dead state. However, we further stream items in
the readyQ from  dead state as well. This commit adds the correct
last seqno sent.

Change-Id: I0f0bfd199544dc5bf20e0ca97b3c5ea8d207c6a8
Reviewed-on: http://review.couchbase.org/64157
Well-Formed: buildbot <build@couchbase.com>
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Manu Dhundi <manu@couchbase.com>