Enable the list of network interfaces.

    Args:
      interfaces: list of string, the output device names to enable.

def EnableNetworkInterfaces(self, interfaces):
    """Enable the list of network interfaces.

    Args:
      interfaces: list of string, the output device names to enable.
    """
    # The default Ethernet interface is enabled by default. Do not attempt to
    # enable interfaces if only one interface is specified in metadata.
    if not interfaces or set(interfaces) == self.interfaces:
      return

    self.logger.info('Ethernet interfaces: %s.', interfaces)
    self.interfaces = set(interfaces)

    if self.dhcp_command:
      try:
        subprocess.check_call([self.dhcp_command])
      except subprocess.CalledProcessError:
        self.logger.warning('Could not enable Ethernet interfaces.')
      return

    # Distro-specific setup for network interfaces.
    self.distro_utils.EnableNetworkInterfaces(
        interfaces, self.logger, dhclient_script=self.dhclient_script)