qemu: Assign device addresses in PostParse
    
    This wires up qemuDomainAssignAddresses into the new
    virDomainDefAssignAddressesCallback, so it's always triggered
    via virDomainDefPostParse. We are essentially doing this already
    with open coded calls sprinkled about.
    
    qemu argv parse output changes slightly since previously it wasn't
    hitting qemuDomainAssignAddresses.