Remove deprecated legacy network info model in Hypervisor drivers

This patch removes legacy network info wihch is unused in any Hypervisor
drivers, clean up related tests and Also removes legacy method from
nova.network.model.

Partly implement blueprint nova-network-legacy

Change-Id: Ia3f11b1a162878817445619575b35187110dafb5
Merge "Remove deprecated legacy network info model in Hypervisor drivers"