test/zdtm.sh: show help if unknown option is used

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm.sh

@@ -698,6 +698,7 @@ while :; do
 		;;
 	  -*)
 		echo "Unrecognized option $1, aborting!" 1>&2
+		usage
 		exit 1
 		;;
 	  *)