Dockerfile: Refactor `make install`
Dockerfile: Don't `ENV DEBIAN_FRONTEND noninteractive`

It's better to export it in the individual rules as otherwise it ends up
in the environment of the commands run.
service: Add command to regenerate authorized_keys file for ssh login
Add Dockerfile for service
Fixup service
service: The docker command is `docker` not `docker.io`

We require docker >1.0 which even on Debian/Ubuntu uses the command
`docker`.
Fixup stbt service running in docker
fix make docker-build
rename service-users-volume
Fix make docker-publish
fixup docker
service: Add documentation