SPARK-1469: Scheduler mode should accept lower-case definitions and h…

…ave nicer error messages

There are  two improvements to Scheduler Mode:
1. Made the built in ones case insensitive (fair/FAIR, fifo/FIFO).
2. If an invalid mode is given we should print a better error message.

core/src/main/scala/org/apache/spark/scheduler/SchedulingMode.scala

@@ -25,5 +25,5 @@ package org.apache.spark.scheduler
 object SchedulingMode extends Enumeration {
 
   type SchedulingMode = Value
-  val FAIR,FIFO,NONE = Value
+  val FAIR, FIFO, NONE = Value
 }

core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala

@@ -98,8 +98,13 @@ private[spark] class TaskSchedulerImpl(
   var schedulableBuilder: SchedulableBuilder = null
   var rootPool: Pool = null
   // default scheduler is FIFO
-  val schedulingMode: SchedulingMode = SchedulingMode.withName(
-    conf.get("spark.scheduler.mode", "FIFO"))
+  private val schedulingModeConf = conf.get("spark.scheduler.mode", "FIFO")
+  val schedulingMode: SchedulingMode = try {
+    SchedulingMode.withName(schedulingModeConf.toUpperCase)
+  } catch {
+    case e: java.util.NoSuchElementException =>
+      throw new SparkException(s"Urecognized spark.scheduler.mode: $schedulingModeConf")
+  }
 
   // This is a var so that we can reset it for testing purposes.
   private[spark] var taskResultGetter = new TaskResultGetter(sc.env, this)