The runtime image was not the last stage thus it was always build and
left as untagged image. We can improve that. Refer to the docs for the
`docker build --target` option:
> Commands after the target stage will be skipped.
Ref: https://docs.docker.com/engine/reference/commandline/build/#specifying-target-build-stage---target
This commit simply moves the dpkg build stage patch above the runtime
image stage.
Robin Schneider