hack/cluster: consolidate cluster/ utils to hack/lib/util.sh
hack/cluster: consolidate cluster/ utils to hack/lib/util.sh

Per Clayton's suggestion, move stuff from cluster/lib/util.sh to
hack/lib/util.sh.  Also consolidate ensure-temp-dir and use the
hack/lib/util.sh implementation rather than cluster/common.sh.

kubernetes-retired/cluster-registry,kubernetes-retired/cluster-registry