Update variable for dns_zone on infra-osp-dns role (#4372)

ansible/roles-infra/infra-osp-dns/tasks/nested_loop.yml

@@ -31,7 +31,7 @@
     - name: Add public_dns entry to host
       add_host:
         name: "{{ _instance_name }}"
-        public_dns_name: "{{ _instance_name }}.{{ guid }}.{{ cluster_dns_zone }}"
+        public_dns_name: "{{ _instance_name }}.{{ guid }}.{{ osp_cluster_dns_zone | default(cluster_dns_zone) }}"
 
     - name: DNS alternative entry ({{ _dns_state | default('present') }})
       when: _alt_names | length > 0