This refactors log-dump.sh so that it can optionally just use "kubectl
get node" output, for dumping logs off a cluster that was brought up
using sometihng other than kube-up.sh (e.g. kops or kubeadm).
Note that for obvious reasons, if the cluster is fried, it'll probably
fail to hit the apiserver and all bets are off, but for the 95% case
where you're debugging tests, this is good. To cover the remaining 5%,
you could actually squirrel away the relevant external IPs after the
e2e.go:Up stage (because we better be able to hit the apiserver then)
and fetch them from cache later.
4338351be2