Add a configuration option for spark-shell's class server

spark.replClassServer.port

Author: ash211

repl/src/main/scala/org/apache/spark/repl/SparkIMain.scala

@@ -102,7 +102,8 @@ import org.apache.spark.util.Utils
 
     val virtualDirectory                              = new PlainFile(outputDir) // "directory" for classfiles
     /** Jetty server that will serve our classes to worker nodes */
-    val classServer                                   = new HttpServer(outputDir, new SecurityManager(conf))
+    val classServerListenPort: Int                    = conf.getInt("spark.replClassServer.port", 0)
+    val classServer                                   = new HttpServer(outputDir, new SecurityManager(conf), classServerListenPort)
     private var currentSettings: Settings             = initialSettings
     var printResults                                  = true      // whether to print result lines
     var totalSilence                                  = false     // whether to print anything