GCE: Don't create utility subnets in private topology

We don't need them on GCE, and in fact we don't support them with IP Alias.

tests/integration/create_cluster/private_gce/expected-v1alpha2.yaml

@@ -52,9 +52,6 @@ spec:
   - name: us-test1
     region: us-test1
     type: Private
-  - name: utility-us-test1
-    region: us-test1
-    type: Utility
   topology:
     bastion:
       bastionPublicName: bastion.private.example.com

upup/pkg/fi/cloudup/new_cluster.go

@@ -980,8 +980,6 @@ func setupTopology(opt *NewClusterOptions, cluster *api.Cluster, allZones sets.S
 			cluster.Spec.Subnets[i].Type = api.SubnetTypePrivate
 		}
 
-		var utilitySubnets []api.ClusterSubnetSpec
-
 		var zoneToSubnetProviderID map[string]string
 		var err error
 		if len(opt.Zones) > 0 && len(opt.UtilitySubnetIDs) > 0 {
@@ -1001,6 +999,16 @@ func setupTopology(opt *NewClusterOptions, cluster *api.Cluster, allZones sets.S
 			}
 		}
 
+		addUtilitySubnets := true
+		switch api.CloudProviderID(cluster.Spec.CloudProvider) {
+		case api.CloudProviderGCE:
+			// GCE does not need utility subnets
+			addUtilitySubnets = false
+		}
+
+		if addUtilitySubnets {
+			var utilitySubnets []api.ClusterSubnetSpec
+
 			for _, s := range cluster.Spec.Subnets {
 				if s.Type == api.SubnetTypeUtility {
 					continue
@@ -1017,6 +1025,7 @@ func setupTopology(opt *NewClusterOptions, cluster *api.Cluster, allZones sets.S
 				utilitySubnets = append(utilitySubnets, subnet)
 			}
 			cluster.Spec.Subnets = append(cluster.Spec.Subnets, utilitySubnets...)
+		}
 
 		if opt.Bastion {
 			bastionGroup := &api.InstanceGroup{}