Don't override the docker url that it found in the env.
Don't override the docker url that it found in the env.

boot2docker sets env vars like this:

    export DOCKER_HOST=tcp://192.168.59.104:2376
    export DOCKER_CERT_PATH=/Users/spraints/.boot2docker/certs/porter
    export DOCKER_TLS_VERIFY=1

The docker-api gem initializes `Docker.url` from these variables. If
boot2docker and docker-api already know what the docker connection is,
we don't need to mess with it in hoosegow.

github/hoosegow,github/hoosegow