[BP] MB-8521 Reset notifySent flag upon vbucket filter changes

When the TAP producer receives the vbucket filter change
request from the cluster manager, it should set notifySent
flag to false, so that the TAP producer can send the TAP
OPAQUE response to the cluster manager immediately in order to
notify that the filter change request was successfully applied.

Otherwise, there can be 5 seconds unnecessary delay in sending
the reponse to the cluster manager.

Change-Id: If8e7720d6d2ff8a71040a95963b2065a4a58686e
Reviewed-on: http://review.couchbase.org/27510
Reviewed-by: Chiyoung Seo <chiyoung.seo@gmail.com>
Tested-by: Chiyoung Seo <chiyoung.seo@gmail.com>