Fix default route in multiple nics net isolation templates

Fix default route in multiple nics net isolation templates

The non-controller nodes in the network/config/multiple-nics
directory do not have a default route configured. This change
adds the default route to the non-controller nodes using the
ControlPlaneDefaultRoute parameter, which was already a part
of these templates.

Change-Id: Idaaeb2a539555ac14cc613b202c428108bc19a30