metropolis/cli/metroctl: don't print usage for runtime errors

Change-Id: I91fdca45e874ea1ec9112df556a9a7392fd45bfd
Fixes: https://github.com/monogon-dev/monogon/issues/352
Reviewed-on: https://review.monogon.dev/c/monogon/+/3440
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/cli/metroctl/cmd_node_approve.go b/metropolis/cli/metroctl/cmd_node_approve.go
index 62ab7bd..294f8c3 100644
--- a/metropolis/cli/metroctl/cmd_node_approve.go
+++ b/metropolis/cli/metroctl/cmd_node_approve.go
@@ -17,7 +17,7 @@
 var approveCmd = &cobra.Command{
 	Short: "Approves a candidate node, if specified; lists nodes pending approval otherwise.",
 	Use:   "approve [node-id]",
-	Args:  cobra.MaximumNArgs(1), // One positional argument: node ID
+	Args:  PrintUsageOnWrongArgs(cobra.MaximumNArgs(1)), // One positional argument: node ID
 	Run:   doApprove,
 }