runsvdir-start clears the environment, which wipes out any
environment variables passed in when the container starts.
This patch bypasses runsvdir-start and calls runsvdir directly,
preserving the current environment.
When a container is stopped with 'docker stop', SIGTERM is sent to the
init process. Unfortunately neither bash nor runit-init handle that correctly,
so we write our own init system in Python that also waits for all services to
shutdown.
