Allow GRID files to point to other links

Currently the CI will check if a GRID file (link) points to eos or cvmfs.
We want to allow the possibility that a link points to another link.

while $(test -L $GRID) ; do 
  GRID=$(readlink $GRID) ; 
done

Alternatively we can replace readlink with readlink -e (if we want to test for the existence of the final file) or readlink -f (if we don't care about testing that the final file exists). Need to see if -e/f are available in the CI image.