set gather_facts to true

playbooks/edx-east/rabbitmq.yml

 - name: Deploy rabbitmq
   hosts: all
   sudo: True
-  gather_facts: False
+  # The rabbitmq role depends on
+  # ansible_default_ipv4 so
+  # gather_facts must be set to True
+  gather_facts: True
   roles:
     - aws
     - rabbitmq