FIX: adapt `migrate_2_2_0()` --> `_migrate_2_2_0()`
FIX: adapt `migrate_2_2_0()` --> `_migrate_2_2_0()`

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