Add check to catch included files which are unreachable

Changes introduced

Add check in check_jo_consistency that throws an error if included files are not reachable

Tests

Included file in same directory

Included file in different directory but with a valid path

Included file in private afs directory

As in #178 (closed)

Included file include('../../513xxx/513444/MadGraphControl_WHjjEW_lvbb.py')

See https://gitlab.cern.ch/atlas-physics/pmg/mcjoboptions/-/jobs/22756527

Included file from cvmfs and accessible: include('/cvmfs/atlas.cern.ch/repo/sw/Generators/MCJobOptions/513xxx/513444/MadGraphControl_WHjjEW_lvbb.py')

https://gitlab.cern.ch/atlas-physics/pmg/mcjoboptions/-/jobs/22756771

Included file from cvmfs but pointing to non-existing location

https://gitlab.cern.ch/atlas-physics/pmg/mcjoboptions/-/jobs/22756783

Issues resolved

Closes #178 (closed)