add tests for .cvmfs_last_gc, and check timestamp in .cvmfs_last_snapshot
add tests for .cvmfs_last_gc, and check timestamp in .cvmfs_last_snapshot

cvmfs/cvmfs,Gangbiao/cvmfs,Gangbiao/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,Gangbiao/cvmfs,cvmfs/cvmfs,djw8605/cvmfs,djw8605/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,djw8605/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,Gangbiao/cvmfs,Gangbiao/cvmfs,djw8605/cvmfs,cvmfs/cvmfs,djw8605/cvmfs,DrDaveD/cvmfs