(GH-8) Configuration for PowerShell Host

By default use the internal PowerShell host. Allow using the system
host either by shutting off the feature or by using a switch
`--use-system-powershell`.

src/chocolatey/infrastructure.app/ApplicationParameters.cs

@@ -101,6 +101,7 @@ public static class Features
             public static readonly string FailOnAutoUninstaller = "failOnAutoUninstaller";
             public static readonly string AllowGlobalConfirmation = "allowGlobalConfirmation";
             public static readonly string FailOnStandardError = "failOnStandardError";
+            public static readonly string UsePowerShellHost = "powershellHost";
         }
 
         public static class Messages

src/chocolatey/infrastructure.app/builders/ConfigurationBuilder.cs

@@ -188,6 +188,7 @@ private static void set_feature_flags(ChocolateyConfiguration config, ConfigFile
             config.Features.AutoUninstaller = set_feature_flag(ApplicationParameters.Features.AutoUninstaller, configFileSettings, defaultEnabled: true, description: "Uninstall from programs and features without requiring an explicit uninstall script.");
             config.Features.FailOnAutoUninstaller = set_feature_flag(ApplicationParameters.Features.FailOnAutoUninstaller, configFileSettings, defaultEnabled: false, description: "Fail if automatic uninstaller fails.");
             config.Features.FailOnStandardError = set_feature_flag(ApplicationParameters.Features.FailOnStandardError, configFileSettings, defaultEnabled: false, description: "Fail if install provider writes to stderr.");
+            config.Features.UsePowerShellHost = set_feature_flag(ApplicationParameters.Features.UsePowerShellHost, configFileSettings, defaultEnabled: true, description: "Use Chocolatey's built-in PowerShell host.");
             config.PromptForConfirmation = !set_feature_flag(ApplicationParameters.Features.AllowGlobalConfirmation, configFileSettings, defaultEnabled: false, description: "Prompt for confirmation in scripts or bypass.");
         }
 
@@ -264,6 +265,9 @@ private static void set_global_options(IList<string> args, ChocolateyConfigurati
                             .Add("failstderr|failonstderr|fail-on-stderr|fail-on-standard-error|fail-on-error-output",
                                  "FailOnStandardError - Fail on standard error output (stderr), typically received when running external commands during install providers. This overrides the feature failOnStandardError.",
                                  option => config.Features.FailOnStandardError = option != null)
+                            .Add("use-system-powershell",
+                                 "UseSystemPowerShell - Execute PowerShell using an external process instead of the built-in PowerShell host.",
+                                 option => config.Features.UsePowerShellHost = option == null)
                             ;
                     },
                 (unparsedArgs) =>

src/chocolatey/infrastructure.app/configuration/ChocolateyConfiguration.cs

@@ -336,6 +336,7 @@ public sealed class FeaturesConfiguration
         public bool CheckSumFiles { get; set; }
         public bool FailOnAutoUninstaller { get; set; }
         public bool FailOnStandardError { get; set; }
+        public bool UsePowerShellHost { get; set; }
     }
 
     //todo: retrofit other command configs this way