SPARK-1176 Add port configuration for HttpBroadcast

Uses spark.broadcast.port

Author: ash211

core/src/main/scala/org/apache/spark/broadcast/HttpBroadcast.scala

@@ -152,7 +152,8 @@ private[broadcast] object HttpBroadcast extends Logging {
 
   private def createServer(conf: SparkConf) {
     broadcastDir = Utils.createTempDir(Utils.getLocalDir(conf))
-    server = new HttpServer(broadcastDir, securityManager)
+    val broadcastListenPort: Int = conf.getInt("spark.broadcast.port", 0)
+    server = new HttpServer(broadcastDir, securityManager, broadcastListenPort)
     server.start()
     serverUri = server.uri
     logInfo("Broadcast server started at " + serverUri)