large refactor/cleanup of most of the old package installer logic dealing with persisting the installedPackages.config which is now in the services, creates new parsers and removes a ton of old code, changes fetching packages to be async, uses XElement instead of old XmlNode apis, next we need to do the actual package installer updates

src/Umbraco.Web/Install/InstallSteps/ConfigureMachineKey.cs

@@ -1,4 +1,5 @@
 using System.Linq;
+using System.Threading.Tasks;
 using System.Web.Configuration;
 using System.Xml.Linq;
 using Umbraco.Core.IO;
@@ -30,7 +31,7 @@ namespace Umbraco.Web.Install.InstallSteps
         /// </summary>
         /// <param name="model"></param>
         /// <returns></returns>
-        public override InstallSetupResult Execute(bool? model)
+        public override Task<InstallSetupResult> ExecuteAsync(bool? model)
         {
             if (model.HasValue && model.Value == false) return null;
 
@@ -50,7 +51,7 @@ namespace Umbraco.Web.Install.InstallSteps
 
             xml.Save(fileName, SaveOptions.DisableFormatting);
 
-            return null;
+            return Task.FromResult<InstallSetupResult>(null);
         }
 
         public override bool RequiresExecution(bool? model)