Added an hostonly interface with fixed ip address for guest and host

With this secondary interface we can now publish ports (`docker run ... -p 8000:80` for instance) without needs to configure new nat rules

The `docker` ip is `172.18.42.1`, the `host` ip is `172.18.42.254`

Since it's a secondary interface, it don't brake anything, you can still use `127.0.0.1:2022` and `127.0.0.1:4243`

TODO:
- [x] Add secondary interface
- [ ] Create an auto-setup for /etc/hosts (like https://github.com/noplay/docker-osx/blob/master/docker-osx#L37-L61)
- [ ] Update the `DOCKER_HOST` in .bashrc ?

cc #85