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/main_test.go

@@ -0,0 +1,76 @@
+package network
+
+import (
+	"fmt"
+	"os"
+	"sync"
+	"testing"
+
+	"github.com/google/uuid"
+	"github.com/pkg/errors"
+	azure "github.com/virtual-kubelet/virtual-kubelet/providers/azure/client"
+	"github.com/virtual-kubelet/virtual-kubelet/providers/azure/client/resourcegroups"
+)
+
+var (
+	location      = "eastus2euap"
+	resourceGroup = "virtual-kubelet-tests"
+	testAuth      *azure.Authentication
+)
+
+func TestMain(m *testing.M) {
+	uid := uuid.New()
+	resourceGroup += "-" + uid.String()[0:6]
+
+	if err := setupAuth(); err != nil {
+		fmt.Fprintln(os.Stderr, "Error setting up auth:", err)
+		os.Exit(1)
+	}
+
+	c, err := resourcegroups.NewClient(testAuth)
+	if err != nil {
+		os.Exit(1)
+	}
+	_, err = c.CreateResourceGroup(resourceGroup, resourcegroups.Group{
+		Name:     resourceGroup,
+		Location: location,
+	})
+	if err != nil {
+		os.Exit(1)
+	}
+
+	code := m.Run()
+
+	if err := c.DeleteResourceGroup(resourceGroup); err != nil {
+		fmt.Fprintln(os.Stderr, "error removing resource group:", err)
+	}
+
+	os.Exit(code)
+}
+
+var authOnce sync.Once
+
+func setupAuth() error {
+	var err error
+	authOnce.Do(func() {
+		testAuth, err = azure.NewAuthenticationFromFile(os.Getenv("AZURE_AUTH_LOCATION"))
+		if err != nil {
+			testAuth, err = azure.NewAuthenticationFromFile("../../../../credentials.json")
+		}
+		if err != nil {
+			err = errors.Wrap(err, "failed to load Azure authentication file")
+		}
+	})
+	return err
+}
+
+func newTestClient(t *testing.T) *Client {
+	if err := setupAuth(); err != nil {
+		t.Fatal(err)
+	}
+	c, err := NewClient(testAuth)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return c
+}