YARN-6287. RMCriticalThreadUncaughtExceptionHandler.rmContext should be final (Contributed by Corey Barker via Daniel Templeton)

(cherry picked from commit e0c239cdbda336e09a35d112d451c2e17d74a3fc)

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

@@ -37,7 +37,7 @@ public class RMCriticalThreadUncaughtExceptionHandler
     implements UncaughtExceptionHandler {
   private static final Log LOG = LogFactory.getLog(
       RMCriticalThreadUncaughtExceptionHandler.class);
-  private RMContext rmContext;
+  private final RMContext rmContext;
 
   public RMCriticalThreadUncaughtExceptionHandler(RMContext rmContext) {
     this.rmContext = rmContext;