Enable the list of network interfaces.

    Args:
      interfaces: list of string, the output device names to enable.
      logger: logger object, used to write to SysLog and serial port.
      dhclient_script: string, the path to a dhclient script used by dhclient.

def EnableNetworkInterfaces(
      self, interfaces, logger, dhclient_script=None):
    """Enable the list of network interfaces.

    Args:
      interfaces: list of string, the output device names to enable.
      logger: logger object, used to write to SysLog and serial port.
      dhclient_script: string, the path to a dhclient script used by dhclient.
    """
    # Should always exist in EL 7.
    if os.path.exists(self.network_path):
      self._DisableNetworkManager(interfaces, logger)
    helpers.CallDhclient(interfaces, logger)