Always require local_alert key argument to have a node.

Change-Id: Ie4ee3ccc1d978a251b1c04f05e5defff0c0e82f9
Reviewed-on: http://review.couchbase.org/37206
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>