acpi-test: retain both asl and aml files on failure

Updated the error message while at it.

Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
acpi-test: issue errors instead of warnings when possible

If the expected (offline) acpi tables loaded correctly,
it is safe to assume the iasl installation is OK and
issue an error if the actual tables differ from expected
ones.

Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>