In atomic, containers are left running when docker is restarted.
When docker is restarted after the flannel config is put in place,
the docker0 interface isn't re-IPed because docker sees the running
containers and won't update the previous config.

This patch kills all the running containers after docker is stopped.
We can't simply `docker stop` the running containers, as they respawn
before we've got a chance to stop the docker daemon, so we need to
use runc to do this after dockerd is stopped.