Do not error out when there are no Docker containers or images

[woopla]

I'm trying to deploy KFD on a set of new VMs, and our default Rocky 8 image is configured with Docker. The Ansible playbook will fail with:

    "docker rm" requires at least 1 argument.
    See 'docker rm --help'.
  
    Usage:  docker rm [OPTIONS] CONTAINER [CONTAINER...]
  
    Remove one or more containers

That's because the output of docker ps -a -q is empty. I've fixed all three calls to go through xargs -r so it's not even trying when there is nothing to delete.