add CoordinatedShutdown, #21537

* CoordinatedShutdown that can run tasks for configured phases in order (DAG)
* coordinate handover/shutdown of singleton with cluster exiting/shutdown
* phase config obj with depends-on list
* integrate graceful leaving of sharding in coordinated shutdown
* add timeout and recover
* add some missing artery ports to tests
* leave via CoordinatedShutdown.run
* optionally exit-jvm in last phase
* run via jvm shutdown hook
* send ExitingConfirmed to leader before shutdown of Exiting
  to not have to wait for failure detector to mark it as
  unreachable before removing
* the unreachable signal is still kept as a safe guard if
  message is lost or leader dies
* PhaseClusterExiting vs MemberExited in ClusterSingletonManager
* terminate ActorSystem when cluster shutdown (via Down)
* add more predefined and custom phases
* reference documentation
* migration guide
* problem when the leader order was sys2, sys1, sys3,
  then sys3 could not perform it's duties and move Leving sys1 to
  Exiting because it was observing sys1 as unreachable
* exclude Leaving with exitingConfirmed from convergence condidtion

akka-cluster/src/multi-jvm/scala/akka/cluster/RestartNodeSpec.scala

@@ -71,8 +71,10 @@ abstract class RestartNodeSpec
 
   lazy val restartedSecondSystem = ActorSystem(
     system.name,
-    ConfigFactory.parseString("akka.remote.netty.tcp.port=" + secondUniqueAddress.address.port.get).
-      withFallback(system.settings.config))
+    ConfigFactory.parseString(s"""
+      akka.remote.netty.tcp.port = ${secondUniqueAddress.address.port.get}
+      akka.remote.artery.canonical.port = ${secondUniqueAddress.address.port.get}
+      """).withFallback(system.settings.config))
 
   override def afterAll(): Unit = {
     runOn(second) {