Use plain messages for notable_event notifications.
Use plain messages for notable_event notifications.

This make sure that misc:flush(notable_event) actually does what it
was intended for.

Change-Id: I08a5e57173b663a72c0a19892a5a6608039fc6ff
Reviewed-on: http://review.couchbase.org/57347
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>

membase/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,ceejatec/ns_server