docs: def restore_configuration_files(self):
          """ restore a previously saved postgresql.conf """
          try:
              for f in self._configuration_to_save:
                  config_file = os.path.join(self._config_dir, f)
                  backup_file = os.path.join(self._data_dir, f + '.backup')
                  if not os.path.isfile(config_file):
                      if os.path.isfile(backup_file):
                          shutil.copy(backup_file, config_file)
                      # Previously we didn't backup pg_ident.conf, if file is missing just create empty
                      elif f == 'pg_ident.conf':
                          open(config_file, 'w').close()
          except IOError:
              logger.exception('unable to restore configuration files from backup')