public RegionMoverBuilder designatedFile(String designatedFile) {
      this.designatedFile = designatedFile;
      return this;
    }
Set the designated file. Designated file contains hostnames where region moves. Designated
file should have 'host:port' per line. Port is mandatory here as we can have many RS running
on a single host.
@param designatedFile The designated file
@return RegionMoverBuilder object
hbase-server/src/main/java/org/apache/hadoop/hbase/util/RegionMover.java