OCPBUGS-33234: azure: bump profile used for network

It seems Azure has added support for multiple address prefixes for a
subnet. This means that getting subnet details might return only
`addressPrefixes` while `addressPrefix` is `nil`. In such cases, the
Installer will fail with a SIGSEGV:
```
$ ../openshift-install create manifests --dir .
INFO Credentials loaded from file "/root/.azure/osServicePrincipal.json"
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x2f7d2e9]

goroutine 1 [running]:
github.com/openshift/installer/pkg/asset/installconfig/azure.validateSubnet({0xc000e1ade8?, 0x237b46b8?}, 0xc000122018?, 0xc000abee40, {0xc000e29d40, 0x28}, {0xc000001080, 0x1, 0x4})
	/go/src/github.com/openshift/installer/pkg/asset/installconfig/azure/validation.go:529 +0x69
github.com/openshift/installer/pkg/asset/installconfig/azure.validateNetworks({0x237e1268, 0xc000015f78}, 0xc0000ced00, {0xc000001080, 0x1, 0x4}, 0xc000a4cde0)
	/go/src/github.com/openshift/installer/pkg/asset/installconfig/azure/validation.go:512 +0x2ff
[...]
```
Let's bump the profile version used from 2018-03-01 to 2020-09-01 so we
can have access to both properties and select the appropriate one.

Author: r4f4

pkg/asset/installconfig/azure/client.go

@@ -7,9 +7,9 @@ import (
 	"strings"
 	"time"
 
-	aznetwork "github.com/Azure/azure-sdk-for-go/profiles/2018-03-01/network/mgmt/network"
 	azres "github.com/Azure/azure-sdk-for-go/profiles/2018-03-01/resources/mgmt/resources"
 	azsubs "github.com/Azure/azure-sdk-for-go/profiles/2018-03-01/resources/mgmt/subscriptions"
+	aznetwork "github.com/Azure/azure-sdk-for-go/profiles/2020-09-01/network/mgmt/network"
 	azenc "github.com/Azure/azure-sdk-for-go/profiles/latest/compute/mgmt/compute"
 	azmarketplace "github.com/Azure/azure-sdk-for-go/profiles/latest/marketplaceordering/mgmt/marketplaceordering"
 	"github.com/Azure/go-autorest/autorest/to"

pkg/asset/installconfig/azure/mock/azureclient_generated.go

@@ -10,7 +10,7 @@ import (
 	"strings"
 
 	azdns "github.com/Azure/azure-sdk-for-go/profiles/2018-03-01/dns/mgmt/dns"
-	aznetwork "github.com/Azure/azure-sdk-for-go/profiles/2018-03-01/network/mgmt/network"
+	aznetwork "github.com/Azure/azure-sdk-for-go/profiles/2020-09-01/network/mgmt/network"
 	azenc "github.com/Azure/azure-sdk-for-go/profiles/latest/compute/mgmt/compute"
 	"github.com/Azure/go-autorest/autorest/to"
 	"github.com/sirupsen/logrus"
@@ -526,7 +526,19 @@ func validateNetworks(client API, p *aztypes.Platform, machineNetworks []types.M
 func validateSubnet(client API, fieldPath *field.Path, subnet *aznetwork.Subnet, subnetName string, networks []types.MachineNetworkEntry) field.ErrorList {
 	allErrs := field.ErrorList{}
 
-	subnetIP, _, err := net.ParseCIDR(*subnet.AddressPrefix)
+	var addressPrefix string
+	switch {
+	case subnet.AddressPrefix != nil:
+		addressPrefix = *subnet.AddressPrefix
+	// NOTE: if the subscription has the `AllowMultipleAddressPrefixesOnSubnet` feature, the Azure API will return a
+	// `addressPrefixes` field with a slice of addresses instead of a single value via `addressPrefix`.
+	case subnet.AddressPrefixes != nil && len(*subnet.AddressPrefixes) > 0:
+		addressPrefix = (*subnet.AddressPrefixes)[0]
+	default:
+		return append(allErrs, field.Invalid(fieldPath, subnetName, "subnet does not have an address prefix"))
+	}
+
+	subnetIP, _, err := net.ParseCIDR(addressPrefix)
 	if err != nil {
 		return append(allErrs, field.Invalid(fieldPath, subnetName, "unable to parse subnet CIDR"))
 	}

pkg/asset/installconfig/azure/validation.go

@@ -5,9 +5,9 @@ import (
 	"net"
 	"testing"
 
-	aznetwork "github.com/Azure/azure-sdk-for-go/profiles/2018-03-01/network/mgmt/network"
 	azres "github.com/Azure/azure-sdk-for-go/profiles/2018-03-01/resources/mgmt/resources"
 	azsubs "github.com/Azure/azure-sdk-for-go/profiles/2018-03-01/resources/mgmt/subscriptions"
+	aznetwork "github.com/Azure/azure-sdk-for-go/profiles/2020-09-01/network/mgmt/network"
 	azenc "github.com/Azure/azure-sdk-for-go/profiles/latest/compute/mgmt/compute"
 	"github.com/Azure/go-autorest/autorest/to"
 	"github.com/golang/mock/gomock"