Clean up generics a bit
ISPN-4951 Entry Retriever iterator should rethrow caused exception

* Pass along any local throwable to iterator
* If remote node receives throwable propagate that as a response
Configure event sender as an async Listener

* Ordering is only guaranteed as long as the async listener executor
is configured with 1 thread, which is the default.
* By using async listener, construction of the event and sending it
is taken out of the critical path of the Hot Rod client request.