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/preinstall/tasks/0100-dhclient-hooks.yml

@@ -1,9 +1,10 @@
 ---
 - name: Configure dhclient to supersede search/domain/nameservers
   blockinfile:
+    # 1 is the 2nd item of a tuple in items()
     block: |-
-      {% for item in [supersede_domain, supersede_search, supersede_nameserver] | reject('equalto', '') -%}
-      {{ item }}
+      {% for key, val in dhclient_supersede.items() | rejectattr(1, '==', []) -%}
+      supersede {{ key }} {{ val | join(',') }};
       {% endfor %}
     path: "{{ dhclientconffile }}"
     create: true