Improve status of dummy job

Changes introduced

When no jO are added the dummy job will report success.
When jO are added but no log.generate.short files are provided the dummy job will give a warning.

Tests

With no jO

Check https://gitlab.cern.ch/atlas-physics/pmg/mcjoboptions/-/jobs/18096337 and the eventual status of this MR

With jO and no log.generate.short file

One of the previous commits in this MR

Issues resolved

Closes #153 (closed)