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/subnet_test.go

@@ -0,0 +1,42 @@
+package network
+
+import "testing"
+
+func TestCreateGetSubnet(t *testing.T) {
+	c := newTestClient(t)
+
+	subnet := &Subnet{
+		Name: t.Name(),
+		Properties: &SubnetProperties{
+			AddressPrefix: "10.0.0.0/24",
+			Delegations: []Delegation{
+				{Name: "aciDelegation", Properties: DelegationProperties{
+					ServiceName: "Microsoft.ContainerInstance/containerGroups",
+					Actions:     []string{"Microsoft.Network/virtualNetworks/subnets/action"},
+				}},
+			},
+		},
+	}
+	ensureVnet(t, t.Name())
+
+	if err := c.CreateOrUpdateSubnet(resourceGroup, t.Name(), subnet); err != nil {
+		t.Fatal(err)
+	}
+
+	s, err := c.GetSubnet(resourceGroup, t.Name(), subnet.Name)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if s.Name != subnet.Name {
+		t.Fatal("got unexpected subnet")
+	}
+	if s.Properties.AddressPrefix != subnet.Properties.AddressPrefix {
+		t.Fatalf("got unexpected address prefix: %s", s.Properties.AddressPrefix)
+	}
+	if len(s.Properties.Delegations) != 1 {
+		t.Fatalf("got unexpected delgations: %v", s.Properties.Delegations)
+	}
+	if s.Properties.Delegations[0].Name != subnet.Properties.Delegations[0].Name {
+		t.Fatalf("got unexpected delegation: %v", s.Properties.Delegations[0])
+	}
+}