Clear shared state pollution to avoid flaky tests

Author: LALAYANG

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

@@ -504,6 +504,7 @@ public void testMRAppMasterCredentials() throws Exception {
   @Test
   public void testMRAppMasterShutDownJob() throws Exception,
       InterruptedException {
+    ExitUtil.resetFirstExitException();
     String applicationAttemptIdStr = "appattempt_1317529182569_0004_000002";
     String containerIdStr = "container_1317529182569_0004_000002_1";
     String userName = "TestAppMasterUser";