[SPARK-10812] [YARN] Fix shutdown of token renewer.

A recent change to fix the referenced bug caused this exception in
the `SparkContext.stop()` path:

org.apache.spark.SparkException: YarnSparkHadoopUtil is not available in non-YARN mode!
        at org.apache.spark.deploy.yarn.YarnSparkHadoopUtil$.get(YarnSparkHadoopUtil.scala:167)
        at org.apache.spark.scheduler.cluster.YarnClientSchedulerBackend.stop(YarnClientSchedulerBackend.scala:182)
        at org.apache.spark.scheduler.TaskSchedulerImpl.stop(TaskSchedulerImpl.scala:440)
        at org.apache.spark.scheduler.DAGScheduler.stop(DAGScheduler.scala:1579)
        at org.apache.spark.SparkContext$$anonfun$stop$7.apply$mcV$sp(SparkContext.scala:1730)
        at org.apache.spark.util.Utils$.tryLogNonFatalError(Utils.scala:1185)
        at org.apache.spark.SparkContext.stop(SparkContext.scala:1729)

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #8996 from vanzin/SPARK-10812.

yarn/src/main/scala/org/apache/spark/scheduler/cluster/YarnClientSchedulerBackend.scala

@@ -178,8 +178,8 @@ private[spark] class YarnClientSchedulerBackend(
       monitorThread.stopMonitor()
     }
     super.stop()
-    client.stop()
     YarnSparkHadoopUtil.get.stopExecutorDelegationTokenRenewer()
+    client.stop()
     logInfo("Stopped")
   }