tests: Hack t_testbed_usb_lsusb for NixOS sandbox
tests: Hack t_testbed_usb_lsusb for NixOS sandbox

In that environment, `lsusb` errors with "Couldn't open device, some
information will be missing" and can't figure out the bus/device name
(they are shown as 0). Make the test more lax in a Nix build for now,
until this gets debugged properly (which is really hard, see
https://github.com/martinpitt/umockdev/issues/115).

martinpitt/umockdev,martinpitt/umockdev,martinpitt/umockdev