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/main.yml

@@ -176,10 +176,10 @@
   when: ansible_os_family == "RedHat"
   register: slc
 
-- name: Set selinux policy to permissive
+- name: Set selinux policy
   selinux:
     policy: targeted
-    state: permissive
+    state: "{{ preinstall_selinux_state }}"
   when:
     - ansible_os_family == "RedHat"
     - slc.stat.exists == True