asset: update dns manifest to use Private DNS Zone

the ingress-operator can handle the Private DNS Zone since [1]

[1]: openshift/cluster-ingress-operator#300

pkg/asset/installconfig/azure/dns.go

@@ -62,6 +62,16 @@ func (config DNSConfig) GetDNSZoneID(rgName string, zoneName string) string {
 		zoneName)
 }
 
+//GetPrivateDNSZoneID returns the Azure Private DNS zone resourceID
+//by interpolating the subscriptionID, the resource group and the zone name
+func (config DNSConfig) GetPrivateDNSZoneID(rgName string, zoneName string) string {
+	return fmt.Sprintf(
+		"/subscriptions/%s/resourceGroups/%s/providers/Microsoft.Network/privateDnsZones/%s",
+		config.Session.Credentials.SubscriptionID,
+		rgName,
+		zoneName)
+}
+
 //GetDNSZone returns a DNS zone selected by survey
 func (config DNSConfig) GetDNSZone() (*Zone, error) {
 	//call azure api using the session to retrieve available base domain

pkg/asset/manifests/dns.go

@@ -98,7 +98,7 @@ func (d *DNS) Generate(dependencies asset.Parents) error {
 			ID: dnsConfig.GetDNSZoneID(installConfig.Config.Azure.BaseDomainResourceGroupName, installConfig.Config.BaseDomain),
 		}
 		config.Spec.PrivateZone = &configv1.DNSZone{
-			ID: dnsConfig.GetDNSZoneID(clusterID.InfraID+"-rg", installConfig.Config.ClusterDomain()),
+			ID: dnsConfig.GetPrivateDNSZoneID(clusterID.InfraID+"-rg", installConfig.Config.ClusterDomain()),
 		}
 	case gcptypes.Name:
 		zone, err := icgcp.GetPublicZone(context.TODO(), installConfig.Config.Platform.GCP.ProjectID, installConfig.Config.BaseDomain)