core: move write_container_id() invocation into initialize_runtime()

core: move write_container_id() invocation into initialize_runtime()

This moves the invocation a bit later, but that shoudln't matter. By
moving it we gain two things: first of all, its closer to other code
where it belongs, secondly its naturally conditioned properly, as we no
longer will rewrite the container ID file on every reexecution again,
and not in test mode either.