daemons expose internal signal number in failure log

[ydirson]

Those "signal -11" occurrences are occasionally visible in the logs:

Oct 14 14:53:21 ydi-xcpng-3-eveeafel xenopsd-xc: [debug||0 ||xenopsd] caught signal -11
Oct 14 14:53:21 ydi-xcpng-3-eveeafel xcp-networkd: [debug||0 |shutdown|network_server] xcp-networkd caught signal -11; performing cleanup actions.

Jan 14 14:51:13 xcp-alma10 xcp-networkd[1764]: [debug||0 |shutdown|network_server] xcp-networkd caught signal -11; performing cleanup actions.

Those are not useful to the reader, we should get more descriptive error messages instead (at least signal name)

[freddy77]

Especially as signal numbers from Ocaml are different from Linux ones. Personally I would be fine with Linux ones too.