guard_interpreter default change for powershell_script, batch resources

This change modifies the default for the `guard_interpreter` attribute for the `batch` and `powershell_script` resources so that for each of these it uses those resources to execute guard expressions by default. That is to say, for `powershell_script`, the `guard_interpreter_attribute` will be set to `:powershell_script` and for the `batch` resource it will be set to `:batch`. 

I think you will need to set the default interpreter as [such](https://github.com/opscode/chef/blob/master/lib/chef/resource/execute.rb#L43) @adamedx. The reason for this is that we need to differentiate between the default interpreter from the interpreter set by the user in order for [this](https://github.com/opscode/chef/blob/master/lib/chef/resource/conditional.rb#L65) error to be raised correctly. 

I think right now if you `:run` a `:windows_script` resource with a pure ruby guard, you will see an error.