FIX: Test 539 Failed due to Permission Problems

The `cvmfs_suid_helper` binary reported an error, because it found `/var/spool/cvmfs/<fqrn>` to be owned by root instead of the repository owner. Saying: "called as 1001, repository owned by 0". In the fixed test case a symlink was created at this location using `sudo ln` and without a `chown` afterwards. Fixed.

However, I find the error message of `cvmfs_suid_helper` slightly misleading. Shouldn't it do a `platform_stat` instead of `platform_lstat` and don't care about the permission of this symlink? Or at least be more specific about what actually is wrong.