Fix typo CVMFS_DEBUG_LOG -> CVMFS_DEBUGLOG
Fix typo CVMFS_DEBUG_LOG -> CVMFS_DEBUGLOG

The variable was spelled incorrectly ("CVMFS_DEBUG_LOG") in a unittest.
This had no impact on test correctness, but the variable should be
consistently named, to avoid confusion when searching through the
project.

DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs