YARN-1481. Reverting addendum patch

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1553995 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/AdminService.java

@@ -174,7 +174,7 @@ public class AdminService extends AbstractService implements
     }
   }
 
-  private boolean isRMActive() {
+  private synchronized boolean isRMActive() {
     return HAServiceState.ACTIVE == rmContext.getHAServiceState();
   }