Before restarting docker, instruct it to kill running
containers when it restarts.
Needs a second docker restart after we restore the original
behavior, otherwise the next time docker is restarted by
an operator, it will unexpectedly bring down all running
containers.
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.
The docker-network environment file masks the new values
put into /etc/systemd/system/docker.service.d/flannel-options.conf
to renumber the docker0 to work correctly with flannel.
Josh Lothian