fixed defect that usage statement does not get print out by the hw commands

git-svn-id: https://svn.code.sf.net/p/xcat/code/xcat-core/trunk@4622 8638fb3e-16cb-4fca-ae20-7b5d299a9bcd

xCAT-server/sbin/xcatd

@@ -764,6 +764,7 @@ sub plugin_command {
 
         unless (@nodes) { #register the plugin in the event of usage
           $handler_hash{$ownmod} = 1;
+          $useglobals = 1;
         }
         my $hdlrcache;
 	if ($hdlrtable) {