HDFS-8067. haadmin prints out stale help messages (Contributed by Ajith S)

(cherry picked from commit 66988476d0)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -330,6 +330,8 @@ Release 2.8.0 - UNRELEASED
     HDFS-8257. Namenode rollingUpgrade option is incorrect in document
     (J.Andreina via vinayakumarb)
 
+    HDFS-8067. haadmin prints out stale help messages (Ajith S via vinayakumarb)
+
 Release 2.7.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DFSHAAdmin.java

@@ -90,7 +90,7 @@ public class DFSHAAdmin extends HAAdmin {
 
   @Override
   protected String getUsageString() {
-    return "Usage: haadmin";
+    return "Usage: haadmin [-ns <nameserviceId>]";
   }
 
   @Override