clu #17565 Invoke OnMemberRemoved callback when

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

akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala

@@ -1133,8 +1133,12 @@ private[cluster] class OnMemberStatusChangedListener(callback: Runnable, status:
 
   override def preStart(): Unit =
     cluster.subscribe(self, to)
-  override def postStop(): Unit =
+
+  override def postStop(): Unit = {
+    if (status == Removed)
+      done()
     cluster.unsubscribe(self)
+  }
 
   def receive = {
     case state: CurrentClusterState ⇒