This change adds Controller NIC configs for the sample NIC config
templates that are compatible with IPv6 on the External network.
These controller-v6.yaml templates include a default route for IPv6
on the External network, and a default route for IPv4 on the Control
Plane. The Heat parameters ExternalNetworkDefaultRoute and
ControlPlaneDefaultRoute are used to set these values.
Change-Id: Ifed8cb359eae1d9d623d3eb2fe40ea8a0d1d889a