Disable host key checking in ansible.cfg

Settiing host_key_checking to False helps alleviate the problems caused
on running the playbook with the undercloud as the target host.

Change-Id: Id8140a6e3a4e17dd665ab4e2d736848c72ba75d6

ansible/ansible.cfg

@@ -6,6 +6,7 @@ fact_caching_connection = /tmp/browbeat_fact_cache
 gathering = smart
 roles_path = ./browbeat/roles:./install/roles:
 timeout = 30
+host_key_checking = False
 [ssh_connection]
 # Load the specific ssh config file in this directory
 ssh_args = -F ssh-config