Re-add regression tests for rh#563450

Added in 2392fae6803b9de4a4761509007c160339d57f50 and removed in
be025369ad622867ecf08d5c9170e8e59d2d6294; now they should work with any
backend, as the device names are normalised and not change the guestfish
output depending on the used backend.

Thanks Richard for the hints.