Add API client for Azure custom vnet (#271)

* Update vendor for azure vent support

* Add support for Azure custom vnets.

Use pointers intead of values. This allows the client to pass back
returned data from Azure.

providers/azure/client/network/client_test.go

@@ -0,0 +1,45 @@
+package network
+
+import (
+	"context"
+	"sync"
+	"testing"
+
+	"github.com/Azure/go-autorest/autorest"
+
+	"github.com/Azure/azure-sdk-for-go/services/network/mgmt/2018-05-01/network"
+	"github.com/Azure/go-autorest/autorest/azure/auth"
+)
+
+var vnetAuthOnce sync.Once
+var azAuth autorest.Authorizer
+
+func ensureVnet(t *testing.T, name string) {
+	vnetAuthOnce.Do(func() {
+		var err error
+		azAuth, err = auth.NewClientCredentialsConfig(testAuth.ClientID, testAuth.ClientSecret, testAuth.TenantID).Authorizer()
+		if err != nil {
+			t.Fatalf("error setting up client auth for vnet create: %v", err)
+		}
+	})
+
+	client := network.NewVirtualNetworksClient(testAuth.SubscriptionID)
+	client.Authorizer = azAuth
+
+	prefixes := []string{"10.0.0.0/24"}
+	result, err := client.CreateOrUpdate(context.Background(), resourceGroup, name, network.VirtualNetwork{
+		Name:     &name,
+		Location: &location,
+		VirtualNetworkPropertiesFormat: &network.VirtualNetworkPropertiesFormat{
+			AddressSpace: &network.AddressSpace{
+				AddressPrefixes: &prefixes,
+			},
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := result.WaitForCompletion(context.Background(), client.Client); err != nil {
+		t.Fatal(err)
+	}
+}