Support for NATed addresses

[bluecmd]

Currently the deploy server hacks around this and does its own resolution of this.

Deploy is doing this:
c.execute(
'SELECT host.ipv4_addr_txt, host.ipv6_addr_txt, option.value FROM '
'host, network LEFT OUTER JOIN option ON '
'option.node_id = network.node_id AND option.name = "nat" '
'WHERE network.node_id = host.network_id AND host.name = ?', (node, ))
(v4, v6, nat) = c.fetchone()
if resolve_nat and nat:
# v4 only supported for NATed networks
result[node] = (nat, None)

I think it makes sense to support this natively