[COOK-4679] Modernize cask provider a bit

[COOK-4679](https://tickets.opscode.com/browse/COOK-4679)
This should actually be implemented in load_current_resource to handle the non-zero return code using `brew cask` to query whether the cask is installed:

```ruby
"/usr/local/bin/brew cask list #{new_resource.name}"
```

If the cask is not installed, the command returns non-zero.