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/tasks/main.yml

@@ -66,7 +66,7 @@
       {{ primaryClusterIP }}
       {%- endif -%}
     upstreamForwardTarget: >-
-      {%- if upstream_dns_servers is defined and upstream_dns_servers | length > 0 -%}
+      {%- if upstream_dns_servers | length > 0 -%}
       {{ upstream_dns_servers | join(' ') }}
       {%- else -%}
       /etc/resolv.conf