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/dnsmasq/tasks/main.yml

@@ -102,7 +102,7 @@
 
 - name: Check for dnsmasq port (pulling image and running container)
   wait_for:
-    host: "{{dns_server}}"
+    host: "{{dnsmasq_dns_server}}"
     port: 53
     timeout: 180
   when: inventory_hostname == groups['kube-node'][0] and groups['kube-node'][0] in ansible_play_hosts