kubernetes/preinstall: dns setting cleanup(dhclient, resolvconf)

We use a lot of facts where variables are enough, and format too early,
which prevent reusing the variables in different contexts.

- Moves set_fact variables to the vars directory, remove unnecessary
 intermediate variables, and render them at usage sites to only do logic
 on native Ansible/Jinja lists.
- Use defaults/ rather than default filters for several variables.

roles/kubernetes-apps/ansible/templates/coredns-config.yml.j2

@@ -68,7 +68,7 @@ data:
 {% endif %}
         }
         prometheus :9153
-        forward . {{ upstream_dns_servers | join(' ') if upstream_dns_servers is defined and upstream_dns_servers | length > 0 else '/etc/resolv.conf' }} {
+        forward . {{ upstream_dns_servers | join(' ') if upstream_dns_servers | length > 0 else '/etc/resolv.conf' }} {
           prefer_udp
           max_concurrent 1000
 {% if dns_upstream_forward_extra_opts is defined %}