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 7b913bc6bc70cf71cd9fb16bf71f239e594d3f71.

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

@@ -459,9 +459,9 @@ public class DebugAdmin extends Configured implements Tool {
       if (!command.name.equals("help")) {
         System.out.println(command.usageText);
       }
+      System.out.println();
+      ToolRunner.printGenericCommandUsage(System.out);
     }
-    System.out.println();
-    ToolRunner.printGenericCommandUsage(System.out);
   }
 
   public static void main(String[] argsArray) throws Exception {