Clustering: RuntimeEx thrown from client DCL kills the DCL actor

If a client AsyncDataChangeListener implementation throws an unexpected runtime exception, the exception gets propagated from the DataChangeListener actor to akka. This essentially kills the DataChangeListener actor or akka disables it as it won't receive any more data changed events.

The DataChangeListener actor should catch and log RuntimeExceptions thrown from the client DCL to prevent one from stopping all subsequent data changed events.