Stop trying to make config directories in Windows specs

FileSetting#to_resource had a provision to not attempt to manage files in /dev,
which effectively stopped spec from trying to make their configuration
directories in /dev/null. However, on Windows, the path turns into something
like C:/dev/null, so the specs were still trying to manage their configuration
directories when this wasn't desired or handled by the spec.

Now, we also exclude management of C:/dev (or similar), to mimic the behavior
on Windows. Because this isn't a standard path (and thus will not be used for
anything else), there seems to be no harm in treating it as though it were
really /dev.

Reviewed-By: Josh Cooper <josh@puppetlabs.com>