Access placement service through internal interface rather than public

Change-Id: Ie26b20bb4012d35bfbcd43440d32c9eac7a471d6
Closes-Bug: #1670673

ansible/roles/nova/templates/nova.conf.j2

@@ -246,4 +246,5 @@ user_domain_name = default
 project_name = service
 project_domain_name = default
 os_region_name = {{ openstack_region_name }}
+os_interface = internal
 {% endif %}