MB-21320: Notify memcached to visit readyQ and get any ready items

MB-21320: Notify memcached to visit readyQ and get any ready items

We should notify memcached to visit readyQ and get any items that were
pushed there during stream creation. Also, we must notify the memcached
about cursor dropping so that it can visit ep-engine and stream any
pending items and do a subsequent stream state change.

This is not a functional fix. It improves performance however.
It is not absolutely necessary to notify immediately as conn manager
will notify eventually.

Change-Id: Id06fc450a20f6d0258fa7c687520dff5f4899a28
Reviewed-on: http://review.couchbase.org/69171
Reviewed-by: Dave Rigby <daver@couchbase.com>
Reviewed-by: Jim Walker <jim@couchbase.com>
Tested-by: buildbot <build@couchbase.com>