Ok so I have a feeling that the issues in CI are related to the simply changing HostIp to HostIP in the PortBinding struct.
As we are using the names verbatim when marshalling to JSON, a simple case change will cause a whole world of pain 😢
I've added a tag to the struct to preserve the old-style JSON, but we should probably use something more JSONy like host-ip and/or add tags to all the external facing structs but that is way outside the scope of this patch...

Updated based on @stevvooe's review

@dave-tucker I would consider code that relies on untagged json structs for serialization to be broken. What tests are broken?

@stevvooe failure was in the integration tests
for example, this one in docker-py... https://github.com/docker/docker-py/blob/8a87001d09852058f08a807ab6e8491d57ca1e88/tests/integration_test.py#L605

My hackaround feels wrong on many levels but I'm not really sure what to do here 😕

@dave-tucker I see. This is very unfortunate that we let an internal struct escape into API. Your fix is acceptable.

LGTM

LGTM