It might happen a container takes time to stop its running process - it
therefore will call "SIGTERM" or "SIGKILL", and conmon will return the
actual process exit code.
Since the exit code won't be 0, it will be marked as "failed" in systemd
Note that 137 is, actually, SIGKILL (137-128 = 9) and 143 is SIGTERM
(143-128 = 15).
While systemd accepts actual SIGTERM by default, it doesn't recognize that
143 exit status. We therefore have to namely point to this status code.
Also, by default, SIGKILL isn't accepted as a valid, successful exit status.
This change will needs to be backported down to stable/train - and
another one will be created against triple-ansible.
(cherry picked from commit