m/cli/metroctl: factor out some helper functions

We will need these to create metroctl-compatible configs from
//metropolis/cluster/launch.

Change-Id: I2705afefb62b7e1b35c87d9753c4ca9c7f534c26
Reviewed-on: https://review.monogon.dev/c/monogon/+/1324
Tested-by: Jenkins CI
Reviewed-by: Mateusz Zalega <mateusz@monogon.tech>
diff --git a/metropolis/cli/metroctl/rpc.go b/metropolis/cli/metroctl/rpc.go
index 9a8903a..8e8ee48 100644
--- a/metropolis/cli/metroctl/rpc.go
+++ b/metropolis/cli/metroctl/rpc.go
@@ -12,8 +12,8 @@
 func dialAuthenticated(ctx context.Context) *grpc.ClientConn {
 	// Collect credentials, validate command parameters, and try dialing the
 	// cluster.
-	ocert, opkey, err := getCredentials()
-	if err == noCredentialsError {
+	ocert, opkey, err := core.GetOwnerCredentials(flags.configPath)
+	if err == core.NoCredentialsError {
 		log.Fatalf("You have to take ownership of the cluster first: %v", err)
 	}
 	if len(flags.clusterEndpoints) == 0 {