azurerm_app_service - adding support for HTTP2

```
$ acctests azurerm TestAccAzureRMAppService_http2Enabled
=== RUN   TestAccAzureRMAppService_http2Enabled
--- PASS: TestAccAzureRMAppService_http2Enabled (98.54s)
PASS
ok  	github.com/terraform-providers/terraform-provider-azurerm/azurerm	98.568s
```

azurerm/resource_arm_app_service.go

@@ -70,6 +70,12 @@ func resourceArmAppService() *schema.Resource {
 							DiffSuppressFunc: ignoreCaseDiffSuppressFunc,
 						},
 
+						"http2_enabled": {
+							Type:     schema.TypeBool,
+							Optional: true,
+							Default:  false,
+						},
+
 						"java_version": {
 							Type:     schema.TypeString,
 							Optional: true,
@@ -597,6 +603,10 @@ func expandAppServiceSiteConfig(d *schema.ResourceData) web.SiteConfig {
 		siteConfig.JavaContainerVersion = utils.String(v.(string))
 	}
 
+	if v, ok := config["http2_enabled"]; ok {
+		siteConfig.HTTP20Enabled = utils.Bool(v.(bool))
+	}
+
 	if v, ok := config["local_mysql_enabled"]; ok {
 		siteConfig.LocalMySQLEnabled = utils.Bool(v.(bool))
 	}
@@ -678,6 +688,10 @@ func flattenAppServiceSiteConfig(input *web.SiteConfig) []interface{} {
 		result["local_mysql_enabled"] = *input.LocalMySQLEnabled
 	}
 
+	if input.HTTP20Enabled != nil {
+		result["http2_enabled"] = *input.HTTP20Enabled
+	}
+
 	result["managed_pipeline_mode"] = string(input.ManagedPipelineMode)
 
 	if input.PhpVersion != nil {

azurerm/resource_arm_app_service_test.go

@@ -131,6 +131,27 @@ func TestAccAzureRMAppService_32Bit(t *testing.T) {
 	})
 }
 
+func TestAccAzureRMAppService_http2Enabled(t *testing.T) {
+	resourceName := "azurerm_app_service.test"
+	ri := acctest.RandInt()
+	config := testAccAzureRMAppService_http2Enabled(ri, testLocation())
+
+	resource.Test(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testCheckAzureRMAppServiceDestroy,
+		Steps: []resource.TestStep{
+			{
+				Config: config,
+				Check: resource.ComposeTestCheckFunc(
+					testCheckAzureRMAppServiceExists(resourceName),
+					resource.TestCheckResourceAttr(resourceName, "site_config.0.http2_enabled", "true"),
+				),
+			},
+		},
+	})
+}
+
 func TestAccAzureRMAppService_alwaysOn(t *testing.T) {
 	resourceName := "azurerm_app_service.test"
 	ri := acctest.RandInt()
@@ -909,6 +930,37 @@ resource "azurerm_app_service" "test" {
 `, rInt, location, rInt, rInt)
 }
 
+func testAccAzureRMAppService_http2Enabled(rInt int, location string) string {
+	return fmt.Sprintf(`
+resource "azurerm_resource_group" "test" {
+  name = "acctestRG-%d"
+  location = "%s"
+}
+
+resource "azurerm_app_service_plan" "test" {
+  name                = "acctestASP-%d"
+  location            = "${azurerm_resource_group.test.location}"
+  resource_group_name = "${azurerm_resource_group.test.name}"
+
+  sku {
+    tier = "Standard"
+    size = "S1"
+  }
+}
+
+resource "azurerm_app_service" "test" {
+  name                = "acctestAS-%d"
+  location            = "${azurerm_resource_group.test.location}"
+  resource_group_name = "${azurerm_resource_group.test.name}"
+  app_service_plan_id = "${azurerm_app_service_plan.test.id}"
+
+  site_config {
+    http2_enabled = true
+  }
+}
+`, rInt, location, rInt, rInt)
+}
+
 func testAccAzureRMAppService_appSettings(rInt int, location string) string {
 	return fmt.Sprintf(`
 resource "azurerm_resource_group" "test" {

website/docs/r/app_service.html.markdown

@@ -127,6 +127,8 @@ The following arguments are supported:
 
 * `https_only` - (Optional) Can the App Service only be accessed via HTTPS? Defaults to `false`. Changing this forces a new resource to be created.
 
+* `http2_enabled` - (Optional) Is HTTP2 Enabled on this App Service? Defaults to `false`. Changing this forces a new resource to be created.
+
 * `site_config` - (Optional) A `site_config` object as defined below.
 
 * `tags` - (Optional) A mapping of tags to assign to the resource. Changing this forces a new resource to be created.