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/vars/main.yml

@@ -76,4 +76,17 @@ coredns_server_by_mode:
   coredns_dual: "{{ [skydns_server, skydns_server_secondary] }}"
   manual: "{{ manual_dns_server.split(',') }}"
   none: []
-coredns_server: "{{ upstream_dns_server if dns_early else coredns_server_by_mode[dns_mode] }}"
+coredns_server: "{{ upstream_dns_servers if dns_early else coredns_server_by_mode[dns_mode] }}"
+
+_nameserverentries:
+  late:
+    - "{{ nodelocaldns_ip if enable_nodelocaldns else coredns_server }}"
+  early:
+    - "{{ nameservers }}"
+    - "{{ cloud_resolver }}"
+    - "{{ configured_nameservers if not disable_host_nameservers else [] }}"
+nameserverentries: "{{ ((_nameserverentries['late'] if not dns_early else []) + _nameserverentries['early']) | flatten | unique }}"
+dhclient_supersede:
+  domain-name-servers: "{{ ([nameservers, cloud_resolver] | flatten | unique) if dns_early else nameserverentries }}"
+  domain-name: "{{ [dns_domain] }}"
+  domain-search: "{{ default_searchdomains + searchdomains }}"