#2778 - make thread names unique per system

The MonitorableThreadFactory.copy method does not take into account the
counter:AtomicLong field, which then always starts out at zero for every
new dispatcher; the PinnedDispatcher creates one dispatcher per actor,
hence resulting in identical thread names if used by multiple actors.
Solution: add the counter to the case class’ arguments

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

@@ -95,7 +95,7 @@ class Cluster(val system: ExtendedActorSystem) extends Extension {
       new DefaultScheduler(
         new HashedWheelTimer(log,
           system.threadFactory match {
-            case tf: MonitorableThreadFactory ⇒ tf.copy(name = tf.name + "-cluster-scheduler")
+            case tf: MonitorableThreadFactory ⇒ tf.withName(tf.name + "-cluster-scheduler")
             case tf                           ⇒ tf
           },
           SchedulerTickDuration,