Remove old legacy network info model in libvirt driver

Update libvirt driver, virt firewall and hypervisor unit tests to
use nova.network.model instead of legacy "network,mapping" tuple.

Partly implement blueprint nova-network-legacy

Co-author: Amir Sadoughi<amir.sadoughi@gmail.com>
Change-Id: I4d38bb81a4f64efdb78f5da52fbbb382981e0b96
Merge "Remove old legacy network info model in libvirt driver"