Addresses Bug 1210257:

https://bugs.launchpad.net/openstack-cisco/+bug/1210257

Since COI currently does not support using a seperate interface
for GRE tunnel endpoints, exposing the tunnel_ip parameter is
unneeded.  Additionally, COI now supports multiple networking
models, so the tunnel_ip requirement is unneeded.

tunnel_ip now defaults to controller_node_internal for the control
class and internal_ip for the compute class.