MB-8861 Schedule a tap connection notification through dispatcher

This change allows us to schedule a notification event for a
given TAP connection through the non-IO dispatcher.

Change-Id: I3ef0ef3c9bcd86293f0114355c064069946c5977
Reviewed-on: http://review.couchbase.org/28334
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung.seo@gmail.com>