Should not use an IPNetwork when assigning floating IPs

Using the iter_hosts() method of an IPNetwork in nova-manage.FloatingIpCommands.address_to_hosts() filters out the first and last IPs, as the documentation on iter_hosts() notes:

>>> help(netaddr.IPNetwork.iter_hosts())
    ...
    - for IPv4, the network and broadcast adresses are always excluded. Any subnet that contains less than 4 IP addresses yields an empty list

For most users, this isn't a problem because usually IP addresses are over-provisioned, but it can lead to a very annoying bug where 'nova-manage floating create 192.168.0.2' works, but 'nova-manage floating create 192.168.0.2/32' and 'nova-manage floating create 192.168.0.2/31' both fail to affect nova's floating_ips table at all.