fix(systemd units): Fix docker containers being orphaned

Docker seems to orphan our containers after the fix in [6b452e](https://github.com/deis/deis/commit/6b452e), this reverts part of it and properly signals the docker containers to stop. Given that we run them with `--rm`, this also makes the ephemeral containers destroy their data off of the drives. The data containers are not affected by this and they persist.

This closes #1378