Passes the token_driver parameter

Supports the following patch:
  https://review.openstack.org/#/c/41784/

Allows the openstack module to pass the token_driver parameter
from the puppet-keystone module.

Exposes the parameter as keystone_token_driver within the
openstack::controller class so users have a better understanding
of what service the token_driver is related to.

Change-Id: Iaf7bf1375ec9ad22b014586aec19474205ca23ab