First step in refactoring of cluster internals to actors, see #2311

* Move clustering code to ClusterCore actor
* More will be done, comitting this for early review

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

@@ -36,6 +36,10 @@ abstract class JoinSeedNodeSpec
 
   "A cluster with configured seed nodes" must {
     "start the seed nodes sequentially" taggedAs LongRunningTest in {
+      // without looking up the addresses first there might be
+      // [akka://JoinSeedNodeSpec/user/TestConductorClient] cannot write GetAddress(RoleName(seed2)) while waiting for seed1
+      roles foreach address
+
       runOn(seed1) {
         startClusterNode()
       }