Two components are added here: a test driver that takes a struct
ratbag_test_device and sets that device up as a ratbag device.
That device is returned to the tests and then checked for sanity.
The ratbag_device_new_test_device() requires the environment variable
RATBAG_TEST set, otherwise we abort. It's also 'hidden' in a separate source
file, so it won't show up in doxygen. And if the test are disabled, this
function does nothing and the test driver never gets registered.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
