Run tests against live Docker

[bfulton]

Especially now that OSX is supported 😸, it's desirable to be able to run tests against a live version of Docker, see #83.

We should use an env var to drive the decision, and experiment with adding Travis CI build matrix support for a couple versions of Docker that aren't in the vcr cassettes.

[nahiluhmot]

👍

[logicminds]

I think Image.json is now broken in 0.8. This would be a great idea to run against a real docker.

Failure/Error: expect(@image.json["container_config"]["ExposedPorts"]).to include("#{port}/tcp")
Excon::Errors::MovedPermanently:
Expected(200..204) <=> Actual(301 Moved Permanently)
# ./spec/image_spec.rb:17:in `block (4 levels) in <top (required)>'