Allow for manual settings for custom docker-machine scenarios.

Running docker commands we can manually specify the host, use tls and certificate requirements. We need to be able to handle custom docker-machine scenarios where we can configure this. I could also see this come in real handy if somebody wanted to monitor remote docker connections (i.e. Azure). Perhaps we can also add a new settings json file to store this in.

DOCKER_TLS_VERIFY=1
DOCKER_HOST=tcp://192.168.99.102:2376 DOCKER_CERT_PATH=C:\Users\myuser\\.docker\machine\machines\default