Cluster Listener Event Batching

Currently when a local listener which was installed for a cluster listener finds an event to send back to the parent it does this 1 message per listener. It might be more beneficial if we had batching so that it wouldn't send 1 message per.

There are 2 cases I can think of which this would benefit.

1. When the underlying transport is UDP. In this case we can send just 1 message to all the nodes for the event instead of N Unicasts
2. When a node has more than 1 cluster listener installed we could send a single message to notifiy more than 1 listener.