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: I65564c23ff0003a575af984c709c1ae365292f35
b4a564795b