test: auto-generate the udev rules

We only ever set properties in the devices, so let's make that more explicit
and auto-generate the udev rule. This way we're hopefully better protected
from the various typos that hid in those rules over the years, but also be
prepared for passing the udev property key/value pairs elsewhere.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>