YARN-3006. Improve the error message when attempting manual failover with auto-failover enabled. (Akira AJISAKA via wangda)

(cherry picked from commit 7d46a806e71de6692cd230e64e7de18a8252019d)
(cherry picked from commit 4151e5729a1ed74ac94035d66876b2dcc52eaaaf)

Conflicts:
	hadoop-yarn-project/CHANGES.txt

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ha/HAAdmin.java

@@ -279,7 +279,13 @@ public abstract class HAAdmin extends Configured implements Tool {
             "supported with auto-failover enabled.");
         return -1;
       }
-      return gracefulFailoverThroughZKFCs(toNode);
+      try {
+        return gracefulFailoverThroughZKFCs(toNode);
+      } catch (UnsupportedOperationException e){
+        errOut.println("Failover command is not supported with " +
+            "auto-failover enabled: " + e.getLocalizedMessage());
+        return -1;
+      }
     }
     
     FailoverController fc = new FailoverController(getConf(),

hadoop-yarn-project/CHANGES.txt

@@ -13,6 +13,9 @@ Release 2.7.1 - UNRELEASED
 
   OPTIMIZATIONS
 
+    YARN-3006. Improve the error message when attempting manual failover with 
+    auto-failover enabled. (Akira AJISAKA via wangda)
+
   BUG FIXES
 
     YARN-3487. CapacityScheduler scheduler lock obtained unnecessarily when