If we have a public & private zone with the same name (which is common
on AWS), this means we can still create records. Also tighten up some
of the logic to allow for zones with duplicate names.
We can put subdomains into hosted zones (for example,
foo.federation.example.com can be hosted in example.com)
By allowing sharing a common hosted zone, this means the user doesn't
have to do as much setup.
