Remove untagged images

[skoch123]

Hello!
How to remove untagged images from docker?

[scotty-c]

I don't believe the module supports removing untagged images, but you can run the following docker rmi $(docker images | grep "^<none>" | awk "{print $3}")

[dbason]

If you're using the latest version of docker you can just do:

docker image prune

[jcrsilva]

You can set this to run on a cron: https://github.com/spotify/docker-gc

Not exactly the same but gets the job done

[gdubicki]

This PR will help to keep only a single tag of a given image: #696