CI: check that mcgensvc has access to eos directories

Currently in check_grid_file_atlcvmfs.sh we are only checking if atlcvmfs has access.
We also need to check if mcgensvc has access, since we are using the mcgensvc credentials when copying GRID files in run_athena.sh, so if mcgensvc does not have access to the eos directory the job will fail.

• Add check for mcgensvc in script
• Add tags:cvmvfs to the check_grid_* jobs