Comment 1 for bug 1769609

There is indeed a regression and the patch for it looks very simple. It can be resumed by below points:

1) Restore the default value for gateway parameter as before in method create_subnet
  gateway=''

2) In create_subnet method where gateway is assigned and restore old behavior:

  if gateway is not None:
    kwargs['gateway_ip'] = str(gateway) or str(subnet_cidr.ip + 1)

3) Remove gateway_ip parameter in below call:

  body = client.create_subnet(
    network_id=network['id'],
    cidr=str(subnet_cidr),
    ip_version=subnet_cidr.version,
    **kwargs)

4) Call it with parameter gateway=None in trunk_test.py (as it was before).