Associate floating IP with router interface

This change will create a dependency from a FloatingIP to a RouterInterface in
this template which interfaces with the same subnet that this FloatingIP's
port is assigned to.

It would be preferable to add the dependency based on matching FloatingIP
floating_network_id and Router external_gateway_info network, but there is
a valid use-case for the Router being external to the template, so the
dependency is matched on the internal subnet instead, which is available
from the RouterInterface property.

Change-Id: Iedff00b382b4fcda741ca5c9b4adc23b176ec48c
Closes-Bug: #1299259
Merge "Associate floating IP with router interface"