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/kubespray-defaults/defaults/main/main.yml

@@ -114,6 +114,10 @@ dns_mode: coredns
 # Enable dns autoscaler
 enable_dns_autoscaler: true
 
+# DNS servers added after the cluster DNS
+# These will also be used as upstream by Coredns for out-cluster queries
+upstream_dns_servers: []
+
 # Enable nodelocal dns cache
 enable_nodelocaldns: true
 enable_nodelocaldns_secondary: false
@@ -137,6 +141,7 @@ dns_domain: "{{ cluster_name }}"
 docker_dns_search_domains:
 - 'default.svc.{{ dns_domain }}'
 - 'svc.{{ dns_domain }}'
+searchdomains: []
 
 kube_dns_servers:
   coredns: ["{{ skydns_server }}"]