Borg handler should detect OOM killing borg
I noticed a strange behaviour, when running a borg backup (see #11347) and tried an reproduce the borg behaviour by running it manually with same options.
This lead to seeing that the return code was 137 (OOM killed).
Looking at the code of the borg handler, it doesn't seem to exhibit an OOM in any particular way.
All I see in the report received by mail is :
... Killed
Fatal: Failed backing up source.
`̀``
Maybe that would be useful to get notified of that particular return code with a specific error message, more verbose than the laconic "killed".
Thanks in adavance.