!clu #15042 useRole restriction on local node is now respected

This is an API breaking change if someone implemented their own Routers.
The change is required because the router must know if the local routees
should be started or not so it has to check the roles of the cluster
member (the local one). We could delay this decision of starting local
routees, but that would allow messages to be dead-letter-ed (bad).

akka-actor/src/main/scala/akka/routing/RouterConfig.scala

@@ -176,10 +176,11 @@ abstract class PoolBase extends Pool
  * them from the router if they terminate.
  */
 trait Pool extends RouterConfig {
+
   /**
    * Initial number of routee instances
    */
-  def nrOfInstances: Int
+  def nrOfInstances(sys: ActorSystem): Int
 
   /**
    * Use a dedicated dispatcher for the routees of the pool.
@@ -315,7 +316,7 @@ class FromConfig(override val resizer: Option[Resizer],
   def withDispatcher(dispatcherId: String): FromConfig =
     new FromConfig(resizer, supervisorStrategy, dispatcherId)
 
-  override val nrOfInstances: Int = 0
+  override def nrOfInstances(sys: ActorSystem): Int = 0
 
   /**
    * [[akka.actor.Props]] for a group router based on the settings defined by