Migrate k8s to kubernetes/client-go

[emilevauge]

The official k8s go client has now its own repository and seems a lot more useful than the old one (kubernetes/kubernetes#11606): https://github.com/kubernetes/client-go
It's time to migrate :)

[ekozan]

the size of the client still ugly :/

[jsravn]

It's large, but handles all known failure cases with the apiserver. I'm not sure traefik's client is correct in this regard. Also, it uses protobuf now which is more efficient than the old json objects (which use of causes memory problems in the apiserver).

[jsravn]

Ah I see this is a duplicate of an issue that covers many more of the problems, ignore me :)

[errm]

This should have been closed when #836 was merged