@Override
  public void setConf(Configuration conf) {
    this.conf = conf;
  }
Map-Reduce implementation of {@link BackupCopyJob}. Basically, there are 2 types of copy
operation: one is copying from snapshot, which bases on extending ExportSnapshot's function, the
other is copying for incremental log files, which bases on extending DistCp's function.
hbase-backup/src/main/java/org/apache/hadoop/hbase/backup/mapreduce/MapReduceBackupCopyJob.java