(GH-560) Load ChocolateyInstaller module from known location

Only load the chocolateyinstaller module and script runner powershell
file from an exact known location. This reduces the chance that it
could be found and used from another location under the Chocolatey
Install directory location.

src/chocolatey/infrastructure.app/services/PowershellService.cs

@@ -97,12 +97,15 @@ public bool uninstall(ChocolateyConfiguration configuration, PackageResult packa
             return run_action(configuration, packageResult, CommandNameType.uninstall);
         }
 
+        private string get_helpers_folder()
+        {
+            return _fileSystem.combine_paths(ApplicationParameters.InstallLocation, "helpers");
+        }
+
         public string wrap_script_with_module(string script, ChocolateyConfiguration config)
         {
-            var installerModules = _fileSystem.get_files(ApplicationParameters.InstallLocation, "chocolateyInstaller.psm1", SearchOption.AllDirectories);
-            var installerModule = installerModules.FirstOrDefault();
-            var scriptRunners = _fileSystem.get_files(ApplicationParameters.InstallLocation, "chocolateyScriptRunner.ps1", SearchOption.AllDirectories);
-            var scriptRunner = scriptRunners.FirstOrDefault();
+            var installerModule = _fileSystem.combine_paths(get_helpers_folder(), "chocolateyInstaller.psm1");
+            var scriptRunner = _fileSystem.combine_paths(get_helpers_folder(), "chocolateyScriptRunner.ps1");
             // removed setting all errors to terminating. Will cause too
             // many issues in existing packages, including upgrading
             // Chocolatey from older POSH client due to log errors