docs: def get_server_model(snmp_client):
      """Get server model of the node.
  
      :param snmp_client: an SNMP client object.
      :raises: SNMPFailure if SNMP operation failed.
      :returns: a string of server model.
      """
  
      try:
          server_model = snmp_client.get(SERVER_MODEL_OID)
          return six.text_type(server_model)
      except SNMPFailure as e:
          raise SNMPServerModelFailure(
              SNMP_FAILURE_MSG % ("GET SERVER MODEL", e))