Refactor use of include_vars
Refactor use of include_vars

Use a first_found lookup instead of a with_first_found loop so that
the 'paths' parameter can be used.

This ensures that only vars from the role are included, and not vars
from a parent calling role. This can happen when a parent role has
a higher priority vars file available for inclusion than the role
it calls.

Change-Id: If97b59759d8f89af371f8b0a4538402b1c3320c1

openstack/openstack-ansible-openstack_hosts,openstack/openstack-ansible-openstack_hosts