TOP-79 create private k8s cluster network

Change containerd runtime to docker. This improves image pull durations, so much so that the local hack to extend the timeouts for setting up the cluster is not required any more.

An unattended installation procedure has also been implemented (https://gitlab.com/deneys.maartens/ska-topic-pxe). This handles much of the configuration steps to the OS that has previously been performed by the playbook in this repo. This merge requests discards all of these OS changes.