MAPREDUCE-7522. Fix SpotBugs issues in hadoop-mapreduce-client-app module.

Author: slfan1989

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/job/impl/TaskAttemptImpl.java

@@ -2551,4 +2551,7 @@ private void initTaskAttemptStatus(TaskAttemptStatus result) {
     result.counters = counters;
   }
 
+  public Container getContainer() {
+    return container;
+  }
 }

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/test/java/org/apache/hadoop/mapreduce/v2/app/TestMRApp.java

@@ -608,7 +608,7 @@ public void handle(ContainerLauncherEvent event) {
         (TaskAttemptImpl) taskAttempts.iterator().next();
     // Container from RM should pass through to the launcher. Container object
     // should be the same.
-    assertSame(taskAttempt.container, containerObtainedByContainerLauncher);
+    assertSame(taskAttempt.getContainer(), containerObtainedByContainerLauncher);
   }
 
   private final class MRAppWithHistory extends MRApp {