Docker requires DOCKER_HOST env to use format localhost:3000 without the scheme

This commit allows a URL to be used that does not contain a scheme.  If detected, the default scheme of `http://` is added.
Reduce context text
First Unix, then http/https/tcp, then all others
Merge pull request #176 from swipely/update-connection-spec

Docker requires DOCKER_HOST env to use format localhost:3000 without the scheme