Make nova_ipam_lib use Network, FixedIP, and FloatingIP objects

This makes nova_ipam_lib use objects for almost everything except
for VIF-related functions, which is coming soon.

Related to blueprint nova-network-objects

Change-Id: Ib39bbc86921eeb849e715a205dccaab3aad6d1c6
Merge "Make nova_ipam_lib use Network, FixedIP, and FloatingIP objects"