Docker machine integration

[hekaldama]

This PR aims to integrate docker-machine to ease local testing of docker-api. It does this by using a (very) lightweight gem called 'docker_machine' to talk to the docker-machine cli, sets up a docker-machine VM, evaluates the VMs docker config bits into the runtime's ENV, and runs the test suite against that VM. This has been tested to be working with bundle exec rake DOCKER_VERSION=1.11.1.

I am unsure if this is the best approach to make docker-api talk to the docker-machine and I am open to other approaches if they would fit better into how docker-api works.

I would like this to be merged sooner rather than later so that I may use it for my docker 1.12.0 updates I am doing for docker-api.

Thanks in advance and please let me know any questions you may have.

[hekaldama]

A TODO on this is to figure out how to use travis CI to do the swarm tests or just mock the docker daemon responses.