YARN-11554. Fix TestRMFailover#testWebAppProxyInStandAloneMode Failed. (#5971)

Author: slfan1989

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-client/src/test/java/org/apache/hadoop/yarn/client/TestRMFailover.java

@@ -212,6 +212,8 @@ public void testAutomaticFailover()
   public void testWebAppProxyInStandAloneMode() throws YarnException,
       InterruptedException, IOException {
     conf.setBoolean(YarnConfiguration.AUTO_FAILOVER_ENABLED, false);
+    conf.set(YarnConfiguration.RM_HA_ID, RM1_NODE_ID);
+
     WebAppProxyServer webAppProxyServer = new WebAppProxyServer();
     try {
       conf.set(YarnConfiguration.PROXY_ADDRESS, "0.0.0.0:9099");