YARN-1498 addendum to fix findbugs warning

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1567483 13f79535-47bb-0310-9956-ffa450edef68

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/SchedulerApplicationAttempt.java

@@ -432,7 +432,7 @@ public class SchedulerApplicationAttempt {
       .transferStateFromPreviousAppSchedulingInfo(appAttempt.appSchedulingInfo);
   }
   
-  public void move(Queue newQueue) {
+  public synchronized void move(Queue newQueue) {
     QueueMetrics oldMetrics = queue.getMetrics();
     QueueMetrics newMetrics = newQueue.getMetrics();
     String user = getUser();