Fix early stop returning errcode -15

[satyaog]

Current log :

benchio.0 [message] Terminating process because it ran for longer than 1 seconds.
benchio.0[end (-15)] 'milabench/bin/voir' --config /tmp/extra/benchio/voirconf-benchio.0-384a97a8bb2d5d89323fc897d5a5d82e.json milabench/tests/yoshua-benchio/main.py --sleep 60 --start 1 --end 11 [at 2024-11-25 15:51:09.910958] benchio.0
=========
  * Error codes = -15
  * No traceback info about the error

instead of

benchio.0 [message] Terminating process because it ran for longer than 1 seconds.
benchio.0 [end] 'milabench/bin/voir' --config /tmp/extra/benchio/voirconf-benchio.0-384a97a8bb2d5d89323fc897d5a5d82e.json milabench/tests/yoshua-benchio/main.py --sleep 60 --start 1 --end 11 [at 2024-11-25 16:00:30.277804] benchio.0
=========
  * early stopped

[Delaunay]

Early stopped and -15 are different.

Early stopped means voir raised StopProgram to crash the benchmark because we don't need more samples;
that is an okay error to ignore, because milabench is causing it on purpose to stop the benchmark

-15 means sigterm was sent to the benchmark because the program ran longer than expected.
This is not okay to ignore because that means the benchmark might be hanging and that is unexpected behavior.
If the benchmark needs more time then its max_duration needs to be increase to reflect its expected runtime