Rename dns_server, add var for selinux. (#1572)

* Rename dns_server to dnsmasq_dns_server so that it includes role prefix
as the var name is generic and conflicts when integrating with existing ansible automation.
*  Enable selinux state to be configurable with new var preinstall_selinux_state

roles/kubernetes/preinstall/tasks/set_resolv_facts.yml

@@ -98,7 +98,7 @@
       {%- elif dns_early|bool -%}
         {{ upstream_dns_servers|default([]) }}
       {%- else -%}
-        {{ [ dns_server ] }}
+        {{ [ dnsmasq_dns_server ] }}
       {%- endif -%}
 
 - name: generate nameservers to resolvconf