m/{cli,test/launch}: integrate launch/cluster with metroctl

This makes test-launch2 (and possibly later any other code that uses the
launch/cluster library) tell the user that they can connect to the newly
launched cluster using metroctl, either by using specific flags, or
using a wrapper script, or using kubectl.

Change-Id: I54035ee02f3cbab3d17f46b1f1685b91aab275a9
Reviewed-on: https://review.monogon.dev/c/monogon/+/1373
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/metropolis/cli/metroctl/k8scredplugin.go b/metropolis/cli/metroctl/k8scredplugin.go
index 605bc87..9b3226e 100644
--- a/metropolis/cli/metroctl/k8scredplugin.go
+++ b/metropolis/cli/metroctl/k8scredplugin.go
@@ -20,8 +20,9 @@
 	Long: `This implements a Kubernetes client-go credential plugin to
 authenticate client-go based callers including kubectl against a Metropolis
 cluster. This should never be directly called by end users.`,
-	Args: cobra.ExactArgs(0),
-	Run:  doK8sCredPlugin,
+	Args:   cobra.ExactArgs(0),
+	Hidden: true,
+	Run:    doK8sCredPlugin,
 }
 
 func doK8sCredPlugin(cmd *cobra.Command, args []string) {