protected void setLastBackupTS(Long ts) {
      this.lastBackupTS = ts;
    }
For each region server: get all log files newer than the last timestamps but not newer than the
newest timestamps.
@param olderTimestamps  the timestamp for each region server of the last backup.
@param newestTimestamps the timestamp for each region server that the backup should lead to.
@param conf             the Hadoop and Hbase configuration
@param savedStartCode   the startcode (timestamp) of last successful backup.
@return a list of log files to be backed up
@throws IOException exception
hbase-backup/src/main/java/org/apache/hadoop/hbase/backup/impl/IncrementalBackupManager.java