Install to workitem root

Author: HaoK

eng/helix/content/RunTests/TestRunner.cs

@@ -121,7 +121,7 @@ public async Task<bool> InstallAspNetAppIfNeededAsync()
             {
                 if (File.Exists(Options.AspNetRuntime))
                 {
-                    var appRuntimePath = $"{Options.DotnetRoot}/shared/Microsoft.AspNetCore.App/{Options.RuntimeVersion}";
+                    var appRuntimePath = $"{Options.HELIX_WORKITEM_ROOT}/shared/Microsoft.AspNetCore.App/{Options.RuntimeVersion}";
                     Console.WriteLine($"Creating directory: {appRuntimePath}");
                     Directory.CreateDirectory(appRuntimePath);
                     Console.WriteLine($"Set ASPNET_RUNTIME_PATH: {appRuntimePath}");
@@ -203,7 +203,7 @@ public bool InstallAspNetRefIfNeeded()
             {
                 if (File.Exists(Options.AspNetRef))
                 {
-                    var refPath = $"{Options.DotnetRoot}/packs/Microsoft.AspNetCore.App.Ref/{Options.RuntimeVersion}";
+                    var refPath = $"{Options.HELIX_WORKITEM_ROOT}/packs/Microsoft.AspNetCore.App.Ref/{Options.RuntimeVersion}";
                     if (Directory.Exists(refPath))
                     {
                         Console.WriteLine($"AspNetRef install skipped: {refPath} already exists.");