FIX: allow umount to fail
FIX: allow umount to fail

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