Docker connection configurable via cfg file

As developer I am using OSX, so I need to run docker in a VM. Dogestry needs to be configured to use the remote API through http not a local socket.

FYI: I am using https://github.com/noplay/docker-osx to wrap up the VM (vagrant) with the native docker client v0.7.3

I am not a Go developer, feel free to make any change and suggestions to my code.