Support both IP and DNS when creating elastic cluster

roles/elastic-stack/ansible-elasticsearch/templates/instances.yml.j2

@@ -4,10 +4,14 @@
 
 {% if node_certs_generator %}
 instances:
-{% for (key,value) in instances.iteritems() %}
+{% for (key,value) in instances.items() %}
 - name: "{{ value.name }}"
+{% if value.ip %}
   ip:
    - "{{ value.ip }}"
-{% endfor %}
+{% elif value.dns %}
-
+  dns:
+   - "{{ value.dns }}"
+{% endif %}
+{% endfor %}
 {% endif %}