Fix an inadvertent 204 in activator tests

On a web server, this test ends up giving back a 204 because of the MVC
behavior when an action is declared to return void. The fix is to use
EmptyResult.

test/WebSites/ActivatorWebSite/Controllers/RegularController.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Mvc;
 
@@ -8,13 +9,15 @@ namespace ActivatorWebSite
 {
     public class RegularController : Controller
     {
-        public void Index()
+        public async Task<EmptyResult> Index()
         {
             // This verifies that ModelState and Context are activated.
             if (ModelState.IsValid)
             {
-                Context.Response.WriteAsync("Hello world").Wait();
+                await Context.Response.WriteAsync("Hello world");
             }
+
+            return new EmptyResult();
         }
     }
 }