[SPARK-12755][CORE] Stop the event logger before the DAG scheduler

[SPARK-12755][CORE] Stop the event logger before the DAG scheduler to avoid a race condition where the standalone master attempts to build the app's history UI before the event log is stopped.

This contribution is my original work, and I license this work to the Spark project under the project's open source license.

Author: Michael Allman <michael@videoamp.com>

Closes #10700 from mallman/stop_event_logger_first.

(cherry picked from commit 4ee8191)
Signed-off-by: Sean Owen <sowen@cloudera.com>

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

@@ -1726,12 +1726,6 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
     Utils.tryLogNonFatalError {
       _executorAllocationManager.foreach(_.stop())
     }
-    if (_dagScheduler != null) {
-      Utils.tryLogNonFatalError {
-        _dagScheduler.stop()
-      }
-      _dagScheduler = null
-    }
     if (_listenerBusStarted) {
       Utils.tryLogNonFatalError {
         listenerBus.stop()
@@ -1741,6 +1735,12 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
     Utils.tryLogNonFatalError {
       _eventLogger.foreach(_.stop())
     }
+    if (_dagScheduler != null) {
+      Utils.tryLogNonFatalError {
+        _dagScheduler.stop()
+      }
+      _dagScheduler = null
+    }
     if (env != null && _heartbeatReceiver != null) {
       Utils.tryLogNonFatalError {
         env.rpcEnv.stop(_heartbeatReceiver)