Improve retrival of external Network (kubernetes#2014)

When attempting to fetch an external Network with IPv4 Subnets to
create a Floating IP, it's possible that no Subnets from that Network
are shared with the tenant, consequently it would not be possible to
filter them by IPVersion and no Network would be used. This commit
improve the detection of external Network by only allowing usage of
Networks that is possible to detect at least one IPV4 Subnet or that
is not possible to detect any info about the Subnets.

Author: MaysaMacedo

pkg/util/openstack/network.go

@@ -27,6 +27,7 @@ import (
 	"github.com/gophercloud/gophercloud/pagination"
 
 	"k8s.io/cloud-provider-openstack/pkg/metrics"
+	cpoerrors "k8s.io/cloud-provider-openstack/pkg/util/errors"
 )
 
 // GetNetworkExtensions returns an extension map.
@@ -89,36 +90,53 @@ func GetFloatingNetworkID(client *gophercloud.ServiceClient) (string, error) {
 		networks.Network
 		external.NetworkExternalExt
 	}
-	var externalNetworks []NetworkWithExternalExt
+	var allNetworks []NetworkWithExternalExt
 
 	mc := metrics.NewMetricContext("network", "list")
 	page, err := networks.List(client, networks.ListOpts{}).AllPages()
 	if err != nil {
 		return "", mc.ObserveRequest(err)
 	}
 
-	err = networks.ExtractNetworksInto(page, &externalNetworks)
+	err = networks.ExtractNetworksInto(page, &allNetworks)
 	if err != nil {
 		return "", mc.ObserveRequest(err)
 	}
-	for _, externalNet := range externalNetworks {
-		if externalNet.External {
+
+	for _, network := range allNetworks {
+		if network.External && len(network.Subnets) > 0 {
 			mc := metrics.NewMetricContext("subnet", "list")
-			page, err := subnets.List(client, subnets.ListOpts{NetworkID: externalNet.ID, IPVersion: 4}).AllPages()
+			page, err := subnets.List(client, subnets.ListOpts{NetworkID: network.ID}).AllPages()
 			if err != nil {
 				return "", mc.ObserveRequest(err)
 			}
 			subnetList, err := subnets.ExtractSubnets(page)
 			if err != nil {
 				return "", mc.ObserveRequest(err)
 			}
-			if len(subnetList) == 0 {
-				continue
+			for _, networkSubnet := range network.Subnets {
+				subnet := getSubnet(networkSubnet, subnetList)
+				if subnet != nil {
+					if subnet.IPVersion == 4 {
+						return network.ID, nil
+					}
+				} else {
+					return network.ID, nil
+				}
 			}
-			return externalNet.ID, nil
 		}
 	}
-	return "", nil
+	return "", mc.ObserveRequest(cpoerrors.ErrNotFound)
+}
+
+// getSubnet checks if a Subnet is present in the list of Subnets the tenant has access to and returns it
+func getSubnet(networkSubnet string, subnetList []subnets.Subnet) *subnets.Subnet {
+	for _, subnet := range subnetList {
+		if subnet.ID == networkSubnet {
+			return &subnet
+		}
+	}
+	return nil
 }
 
 // GetPorts gets all the filtered ports.