Build image when not available

[peteruithoven]

It would be nice if setup could automatically build the image when it isn't available (locally or online).

[peteruithoven]

The difficult part is checking when not to do it. docker images with a filter could be used to check whether a image exists locally. But checking whether it exists in docker-hub is more tricky.

• docker search is quite flexible and will return irrelevant matches.
• docker pull might work, but we should only do this in the setup (not in build, because otherwise it will re-download the image every time).
• Attempting a docker run and when that fails building the image feels wrong. It might fail for other reasons.