add `cvmfs_suid_helper clear_scratch_async <fqrn>`
add `cvmfs_suid_helper clear_scratch_async <fqrn>`

Gangbiao/cvmfs,cvmfs/cvmfs,reneme/cvmfs,DrDaveD/cvmfs,djw8605/cvmfs,trshaffer/cvmfs,Gangbiao/cvmfs,alhowaidi/cvmfsNDN,Gangbiao/cvmfs,alhowaidi/cvmfsNDN,trshaffer/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,reneme/cvmfs,cvmfs/cvmfs,trshaffer/cvmfs,alhowaidi/cvmfsNDN,DrDaveD/cvmfs,Gangbiao/cvmfs,djw8605/cvmfs,DrDaveD/cvmfs,reneme/cvmfs,DrDaveD/cvmfs,djw8605/cvmfs,djw8605/cvmfs,alhowaidi/cvmfsNDN,Gangbiao/cvmfs,djw8605/cvmfs,reneme/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,alhowaidi/cvmfsNDN,cvmfs/cvmfs,cvmfs/cvmfs,trshaffer/cvmfs,reneme/cvmfs,cvmfs/cvmfs,trshaffer/cvmfs