Allow specifying container IP with docker driver

[clinta]

The ability to specify a container IP was added in docker 1.13.0. This PR exposes those options to nomad.

[dadgar]

What is the use case of this?

[clinta]

We run dns servers in docker containers which need to be started with a specific IP addresses. We've been doing this with docker for quite a while, but would like to start using nomad to schedule our containers on our hosts.

[dadgar]

And to be clear this is in a docker, user defined network?

[clinta]

That is how we use it, yes. But the --ip and --ip6 options for docker are supported for all network types.

https://docs.docker.com/engine/reference/run/#network-settings

[dadgar]

@clinta we will probably want to restrict that to non "host" networks. Otherwise the scheduler will be incorrectly accounting IPs.

[clinta]

Actually, I was wrong. The documentation does not indicate that there are any restrictions, but I just tried it for testing and it is indeed only permitted on user defined networks.

docker run --net=host --rm --ip 192.168.10.5 busybox
docker: Error response from daemon: user specified IP address is supported on user defined networks only.

[dadgar]

Can you update this make it clear that it only works on user defined networks.

[dadgar]

Thanks!

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