private List<String> readServersFromFile(String filename) throws IOException {
    List<String> servers = new ArrayList<>();
    if (filename != null) {
      try {
        Files.readAllLines(Paths.get(filename)).stream().map(String::trim)
          .filter(((Predicate<String>) String::isEmpty).negate()).map(String::toLowerCase)
          .forEach(servers::add);
      } catch (IOException e) {
        LOG.error("Exception while reading servers from file,", e);
        throw e;
      }
    }
    return servers;
  }
@param filename The file should have 'host:port' per line
@return List of servers from the file in format 'hostname:port'.
hbase-server/src/main/java/org/apache/hadoop/hbase/util/RegionMover.java