If run_qemu() exits with non-zero, this either meant that QEMU was not
available (which should be a SKIP) or that QEMU timed out if $QEMU_TIMEOUT was
set (which then should be a FAIL).
Limit the exit code of run_qemu() to QEMU availability only, and track timeouts
separately through the new $TIMED_OUT variable, which is then checked in
check_result_qemu().
Do the same for $NSPAWN_TIMEOUT and run_nspawn() so that nspawn and QEMU work
similarly.
Martin Pitt
b2ecd099dc