Revert "Remove duplicate generic usage information to hdfs debug command (#3576). Contributed by daimin."

Misses Jira ID in the commit Message: HDFS-16282
This reverts commit 7b913bc6bc.

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

@@ -459,10 +459,10 @@ public class DebugAdmin extends Configured implements Tool {
       if (!command.name.equals("help")) {
         System.out.println(command.usageText);
       }
-    }
       System.out.println();
       ToolRunner.printGenericCommandUsage(System.out);
     }
+  }
 
   public static void main(String[] argsArray) throws Exception {
     DebugAdmin debugAdmin = new DebugAdmin(new Configuration());