Sync clock using ntpdate.

  Args:
    logger: logger object, used to write to SysLog and serial port.

def CallNtpdate(logger):
  """Sync clock using ntpdate.

  Args:
    logger: logger object, used to write to SysLog and serial port.
  """
  ntpd_inactive = subprocess.call(['service', 'ntpd', 'status'])
  try:
    if not ntpd_inactive:
      subprocess.check_call(['service', 'ntpd', 'stop'])
    subprocess.check_call(
        'ntpdate `awk \'$1=="server" {print $2}\' /etc/ntp.conf`', shell=True)
    if not ntpd_inactive:
      subprocess.check_call(['service', 'ntpd', 'start'])
  except subprocess.CalledProcessError:
    logger.warning('Failed to sync system time with ntp server.')
  else:
    logger.info('Synced system time with ntp server.')