As we mount the kiwix-build (source) directory at run, the docker images
are independent of the source. This will greatly reduce the number of
docker images we have to create.
- Use the same structure than xenial dockerfile.
- Do not try to deploy in the docker image as the deployement is made on
the host.
- Use user `ci_builder` instead of `builder` as it make flatpak fail.
Matthieu Gautier
Kelson