MB-10640: testrunner uprclient send snap_start/end

update stream_request protocol
instead of high_seqno, start|end_seqno is sent for stream request
https://github.com/couchbaselabs/cbupr/blob/master/commands/stream-request.md

Change-Id: I96958a31ec4497cb9613bbacfa9cac6c44d63fbe
Reviewed-on: http://review.couchbase.org/37850
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Tommie McAfee <tommie@couchbase.com>