MB-11579: Add an upr flag to stream to the latest seqno in the vbucket

The "latest" flag will set the end seqno equal to the current high
seqno for the vbucket requested.

Change-Id: Ic0fc3d47bd8c372b173fbf4c1a224fffaf47ac02
Reviewed-on: http://review.couchbase.org/38944
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>