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: I2170bbb9b5e1997aefdcfc9fa6d3700c233a959f
Reviewed-on: http://review.couchbase.org/38936
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>