Address #6075: Shoot the master VM while saving the master-pd. This
takes a couple of minor changes to configure-vm.sh, some of which also
would be necessary for reboot. In particular, I changed it so that the
kube-token instance metadata is no longer required after inception;
instead, we mount the master-pd and see if we've already created the
known tokens file before blocking on the instance metadata.
Also partially addresses #6099 in bash by refactoring the kube-push
path.
