Change @DoNotHydrate to work on fields, not types.

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.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135792416

java/google/registry/model/host/HostResource.java

@@ -89,6 +89,7 @@ public class HostResource extends EppResource implements ForeignKeyedEppResource
   @Index
   @IgnoreSave(IfNull.class)
   @XmlTransient
+  @DoNotHydrate
   Key<DomainResource> superordinateDomain;
 
   /**