* Without a reference a Digital Ocean tag object, terraform may
try to create a firewall rule before a tag actually exists. By
referencing the actual tag objects, the dependency order is
implied
* Remove k8s_domain_name input variable, the controller DNS
record will be "${var.cluster_name}.${dns_zone}"
* Rename dns_base_zone to dns_zone
* Rename dns_base_zone_name to dns_zone_name
* Kubelets should register nodes via their private IPv4 address,
as provided by the metadata service from Digital Ocean
* By default, Kubelet exec's hostname to determine the name it should
use when registering with the apiserver. On Digital Ocean, the hostname
is not routeable by other instances. Digital Ocean does not run an
internal DNS service.
* Fixes issue where the apiserver can't reach the worker nodes. This
prevented kubectl logs and exec commands from working
