UPR: stream_close returns success even after stream_end is received by the consumer

If a stream for a vbucket is requested for a range of seqno (x to y) and the consumer receives docs for all the sequence numbers requested as well as stream_end message, if a stream_close is requested, the ep-engine should return stream-not-found rather than success.

Steps to reproduce:
1. Load beer sample
2. Request vbucket 5 stream for seq number 0 to 3 and read all mutations up to stream_end.
3. Request stream_close for vbucket 5 and you will receive stream_close OK.

Please find the packet trace attached (memcached port 12000)