There was a circular reference when hydrating a domain with a
subordinate host, since the host references the domain. To fix
this, I redid @DoNotHydrate to be the way it should have been,
rather than the hack I had originally submitted. I also beefed
up the unit tests of the epp resource types to check for cycles.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135792416
cgoldfeder
cb8320ff40