Add check if all the hostnames are resolvable

Rabbitmq can't work with IPs, so we need to make sure that all
rabbit cluster hosts can resolve each others hostnames. We
should also require that in docs.

DocImpact
Closes-Bug: #1559158

Change-Id: I2418187138988d21da3dc3624e9cdbda891d4894

ansible/roles/rabbitmq/tasks/bootstrap.yml

 ---
+- name: Check if all rabbit hostnames are resolvable
+  command: "getent hosts {{ hostvars[item]['ansible_hostname'] }}"
+  changed_when: false
+  register: rabbitmq_hostnames
+  with_items: groups['rabbitmq']
+
+- fail: msg="Hostname has to resolve to IP address of api_interface"
+  with_items: rabbitmq_hostnames.results
+  when: "{% set ip=item.stdout.split(' ')[0] %}'{{ hostvars[item['item']]['ansible_' + hostvars[item['item']]['api_interface']]['ipv4']['address'] }}' != '{{ ip }}'"
+
 - name: Creating rabbitmq volume
   kolla_docker:
     action: "create_volume"