Make LocalSparkCluster use distinct IPs

core/src/main/scala/spark/deploy/LocalSparkCluster.scala

@@ -35,11 +35,15 @@ class LocalSparkCluster(numSlaves: Int, coresPerSlave: Int, memoryPerSlave: Int)
 
     /* Start the Slaves */
     for (slaveNum <- 1 to numSlaves) {
+      /* We can pretend to test distributed stuff by giving the slaves distinct hostnames.
+         All of 127/8 should be a loopback, we use 127.100.*.* in hopes that it is
+         sufficiently distinctive. */
+      val slaveIpAddress = "127.100.0." + (slaveNum % 256)
       val (actorSystem, boundPort) = 
-        AkkaUtils.createActorSystem("sparkWorker" + slaveNum, localIpAddress, 0)
+        AkkaUtils.createActorSystem("sparkWorker" + slaveNum, slaveIpAddress, 0)
       slaveActorSystems += actorSystem
       val actor = actorSystem.actorOf(
-        Props(new Worker(localIpAddress, boundPort, 0, coresPerSlave, memoryPerSlave, masterUrl)),
+        Props(new Worker(slaveIpAddress, boundPort, 0, coresPerSlave, memoryPerSlave, masterUrl)),
         name = "Worker")
       slaveActors += actor
     }