jobs: Abort when systemd's event loop lost

When sd_event_prepare returns an error there is currently
no way to restore the event loop working.

It happens when a callback of an sd_event is faulty
(ex: SIGSEGV). In that case the monitoring of signals
(sig-monitor) interfer badly with systemd. But at the
the application firstly has error.

To avoid flooding the journal with messages, aborting
is the best solution.

Bug-AGL: SPEC-1681

Change-Id: If01295f07b3c3fc8c8ec1ac5bf04840d42ee9774
Signed-off-by: José Bollo <jose.bollo@iot.bzh>