profile/systemd-osc-context: Acknowledge uncertainty

profile/systemd-osc-context: Acknowledge uncertainty

Bash does not provide an easy way to discern if an exit status came from
a signal, or was a legitimate non-zero exit (i.e. a failure).  It can be
done, by using job control or by invoking another program; however, such
approaches require modifying the command entered by a user and are, thus,
invasive and risky.

Since an exit status of 129 on a command could either indicate it exited
cleanly with `exit(129)` or was interrupted by `SIGHUP`, the osc context
should report both possibilities, to acknowledge our uncertainty.  Given
we have no idea what happened, besides an unsuccessful exit, the exit is
described as `exit=failure`.

Moreover, discerning between an `interrupt` and a `crash` with a command
likely involves categorizing every signal.  It is fairly obvious `SIGINT`
is an interrupt and also obvious, IMO, that `SIGSEGV` is a crash.  Avoid
the complication (and potential disagreements) by using the encompassing,
generic value — one that remains true if no signal occurred.

References:
 [0] https://stackoverflow.com/a/66431355