cluster.shutdown
* must also be done when the listener actor stops before the
MemberRemoved event has been received
* add test for this
* clarify docs with example that shuts down actor system and
exit jvm
* Getter for CurrentClusterState in Cluster extension, updated via
ClusterReadView
* Remove lazy init of readView. Otherwise the cluster.state will be
empty on first access, wich is probably surprising
* Subscribe to several cluster event types at once, to ensure *one*
CurrentClusterEvent followed by change events
* Deprecate publishCurrentClusterState, was a bad idea, use sendCurrentClusterState
instead
* Possibility to subscribe with InitialStateAsEvents to receive events corresponding
to CurrentClusterState
* CurrentClusterState not a ClusterDomainEvent, ticket #3614
