Fix behaviour of commit script when copying links

Description of bug

When the commit script was moved to the python version oldLinkedFile.startswith('/eos') was replaced with oldLinkedFile.startswith('/'), so links that would incorrectly point to users' directories with a full path would not be correctly copied when assigning DSIDs in the commit script.

Changes introduced

Now the commit script will throw an error if an absolute path is found that is not pointing to cvmfs or eos. This should be enough to catch incorrect linking. (pointing to cvmfs and eos should be allowed for gridpacks)

There is also an edge case merge_LHE.py -> /cvmfs/atlas.cern.ch/repo/sw/Generators/MCJobOptions/501xxx/501716/merge_LHE.py which we don't flag as an error.

Tests

Issues resolved

Closes #