Spark shell exits if it cannot create SparkContext

Mainly, this occurs if you provide a messed up MASTER url (one that doesn't match one
of our regexes). Previously, we would default to Mesos, fail, and then start the shell
anyway, except that any Spark command would fail.

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -217,21 +217,20 @@ class SparkContext(
         scheduler.initialize(backend)
         scheduler
 
-      case _ =>
-        if (MESOS_REGEX.findFirstIn(master).isEmpty) {
-          logWarning("Master %s does not match expected format, parsing as Mesos URL".format(master))
-        }
+      case MESOS_REGEX(mesosUrl) =>
         MesosNativeLibrary.load()
         val scheduler = new ClusterScheduler(this)
         val coarseGrained = System.getProperty("spark.mesos.coarse", "false").toBoolean
-        val masterWithoutProtocol = master.replaceFirst("^mesos://", "")  // Strip initial mesos://
         val backend = if (coarseGrained) {
-          new CoarseMesosSchedulerBackend(scheduler, this, masterWithoutProtocol, appName)
+          new CoarseMesosSchedulerBackend(scheduler, this, mesosUrl, appName)
         } else {
-          new MesosSchedulerBackend(scheduler, this, masterWithoutProtocol, appName)
+          new MesosSchedulerBackend(scheduler, this, mesosUrl, appName)
         }
         scheduler.initialize(backend)
         scheduler
+
+      case _ =>
+        throw new SparkException("Could not parse Master URL: '" + master + "'")
     }
   }
   taskScheduler.start()

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

@@ -845,7 +845,14 @@ class SparkILoop(in0: Option[BufferedReader], val out: PrintWriter, val master:
     val jars = Option(System.getenv("ADD_JARS")).map(_.split(','))
                                                 .getOrElse(new Array[String](0))
                                                 .map(new java.io.File(_).getAbsolutePath)
-    sparkContext = new SparkContext(master, "Spark shell", System.getenv("SPARK_HOME"), jars)
+    try {
+      sparkContext = new SparkContext(master, "Spark shell", System.getenv("SPARK_HOME"), jars)
+    } catch {
+      case e: Exception =>
+        e.printStackTrace()
+        echo("Failed to create SparkContext, exiting...")
+        sys.exit(1)
+    }
     sparkContext
   }