Terraform 0.12 broke compatability and this could result in data loss
if we deleted the etcd volumes. Document the procedure to fix the
tfstate, and require an env var to be passed to avoid accidental data
loss.
We don't call klog.InitFlags yet, because that will cause a flag
redefinition error until we get everyone to stop using glog. That
will happen when we update to k8s 1.13.
* Zones are now subnets
* Utility subnet is no longer part of Zone
* Bastion InstanceGroup type added instead
* Etcd clusters defined in terms of InstanceGroups, not zones
* AdminAccess split into SSHAccess & APIAccess
* Dropped unused Multizone flag
* GCE support only
* Key and secret generation
* "Direct mode" makes API calls
* "Dry run mode" previews the changes
* Terraform output (though key generation not working for master ip)
* cloud-init output (though debian image does not ship with cloud-init)