Improve success message in support register cmd (#4108)

Change the success message on cluster registration to `{alias}
registered successfully`.

When the `mc support register` command is run for an already registered
cluster, show the message `{alias} updated successfully` to indicate
that updated information about the cluster was sent to SUBNET.

cmd/subnet-utils.go

@@ -434,18 +434,11 @@ func getSubnetAccID(headers map[string]string) (string, error) {
 
 // registerClusterOnSubnet - Registers the given cluster on SUBNET
 func registerClusterOnSubnet(alias string, clusterRegInfo ClusterRegistrationInfo) (string, error) {
-	e := setSubnetProxyFromConfig(alias)
+	apiKey, lic, e := getSubnetCreds(alias)
 	if e != nil {
 		return "", e
 	}
 
-	apiKey := getSubnetAPIKeyFromConfig(alias)
-
-	lic := ""
-	if len(apiKey) == 0 {
-		lic = getSubnetLicenseFromConfig(alias)
-	}
-
 	regURL, headers, e := subnetURLWithAuth(subnetRegisterURL(), apiKey, lic)
 	if e != nil {
 		return "", e
@@ -460,6 +453,22 @@ func registerClusterOnSubnet(alias string, clusterRegInfo ClusterRegistrationInf
 	return subnetPostReq(regURL, reqPayload, headers)
 }
 
+func getSubnetCreds(alias string) (string, string, error) {
+	e := setSubnetProxyFromConfig(alias)
+	if e != nil {
+		return "", "", e
+	}
+
+	apiKey := getSubnetAPIKeyFromConfig(alias)
+
+	lic := ""
+	if len(apiKey) == 0 {
+		lic = getSubnetLicenseFromConfig(alias)
+	}
+
+	return apiKey, lic, nil
+}
+
 // extractAndSaveAPIKey - extract api key from response and set it in minio config
 func extractAndSaveAPIKey(alias string, resp string) {
 	subnetAPIKey := gjson.Parse(resp).Get("api_key").String()