Docker goodies

Attach to a running container

• http://askubuntu.com/questions/505506/how-to-get-bash-or-ssh-into-a-running-container-in-background-mode
• http://askubuntu.com/a/507009/129227

Remove untagged docker images

http://stackoverflow.com/a/28377696/1497139

docker rmi -f $(docker images -f "dangling=true" -q)

Support for build env variables

Upcoming feature in 1.9?

• https://github.com/docker/docker/issues/6822