fix cleanup of dns unit test
fix cleanup of dns unit test

MicBrain/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,reneme/cvmfs,DrDaveD/cvmfs,MicBrain/cvmfs,djw8605/cvmfs,cvmfs-testing/cvmfs,cvmfs-testing/cvmfs,Gangbiao/cvmfs,cvmfs-testing/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,reneme/cvmfs,Gangbiao/cvmfs,DrDaveD/cvmfs,Moliholy/cvmfs,djw8605/cvmfs,djw8605/cvmfs,reneme/cvmfs,trshaffer/cvmfs,trshaffer/cvmfs,MicBrain/cvmfs,Moliholy/cvmfs,Gangbiao/cvmfs,cvmfs-testing/cvmfs,trshaffer/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,alhowaidi/cvmfsNDN,cvmfs/cvmfs,reneme/cvmfs,Moliholy/cvmfs,djw8605/cvmfs,trshaffer/cvmfs,DrDaveD/cvmfs,MicBrain/cvmfs,DrDaveD/cvmfs,Gangbiao/cvmfs,cvmfs/cvmfs,alhowaidi/cvmfsNDN,reneme/cvmfs,Moliholy/cvmfs,Gangbiao/cvmfs,alhowaidi/cvmfsNDN,djw8605/cvmfs,MicBrain/cvmfs,trshaffer/cvmfs,alhowaidi/cvmfsNDN,alhowaidi/cvmfsNDN,Moliholy/cvmfs,cvmfs-testing/cvmfs,cvmfs/cvmfs