Sometimes the plugin will want to influence the subclassed device, for instance
by reading a per-plugin config file. At the moment there's no way to do this,
as even _device_registered() is explicitly designed for devices *not* created
by the plugin itself.
Even if _device_registered() was changed to include the plugin creating the
object it would still happen well after the device has done _probe() and/or
_setup() and would probably be too late to do anything useful.
