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`. 

It took me a second to get this.

Currently: ``guard_interpreter :default``
Chef 12: ``guard_interpreter :powershell_script``

However, per @lamont-granquist's point, it would be good to have an option called "shell" or such, as the default behavior is to use the systems shell, e.g. sh or starting a process directly (via mixlib-shellout) on linux or cmd.exe on Windows. :shell would be the same as :default for backward compatibility. (or we could just switch :default to :shell, since this is a major release anyway).

Proposed: ``guard_interpreter :shell`` to get the existing behavior.