Avoid duplicating nameservers (#4833)

roles/kubernetes/preinstall/tasks/0040-set_facts.yml

@@ -141,9 +141,9 @@
 - name: generate nameservers to resolvconf
   set_fact:
     nameserverentries:
-      nameserver {{ ( coredns_server + nameservers|d([]) + cloud_resolver|d([])) | join(',nameserver ') }}
+      nameserver {{ ( coredns_server + nameservers|d([]) + cloud_resolver|d([])) | unique | join(',nameserver ') }}
     supersede_nameserver:
-      supersede domain-name-servers {{ ( coredns_server + nameservers|d([]) + cloud_resolver|d([])) | join(', ') }};
+      supersede domain-name-servers {{ ( coredns_server + nameservers|d([]) + cloud_resolver|d([])) | unique | join(', ') }};
 
 - name: gather os specific variables
   include_vars: "{{ item }}"