add unit test stub for download module
add unit test stub for download module

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