Setting public_address=True gives spurious error

[hartmans]

@timrcm noticed that setting public_address=True in a v4_config gives instance:hypervisor interface eth0 has public address that cannot be assigned
What's going on is that the code is trying to treat True as an IpAddress, look it up to find a AddressAllocation, and use it as an elastic IP.
The code should be updated to only try doing that to IpAddresses not bools.
Everything works; the code still looks at whether bool(public_address) to decide whether to actually associate a public address.