common: don't overwrite failed on success
common: don't overwrite failed on success

If the test failed, but the server did shut down normally, the result is
still a failure. Likewise, a successful test after a failure is still a
failure.

Signed-off-by: Peter Hutterer <b9c50af7afa7642f6f854434cda9ffe54ece8b85@who-t.net>

freedesktop-unofficial-mirror/xorg__test__xorg-integration-tests,freedesktop-unofficial-mirror/xorg__test__xorg-integration-tests,freedesktop-unofficial-mirror/xorg__test__xorg-integration-tests