Improve RDE error logging

RDE logs somewhat inscrutable errors when XML validation of the output fails due to bad data in Datastore. This CL adds a little more information to help us track down this sort of problem in the future.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=140872462

java/google/registry/rde/RdeMarshaller.java

@@ -148,7 +148,7 @@ public final class RdeMarshaller implements Serializable {
           Key.create(resource),
           e.getLinkedException(),
           getMarshaller().marshalLenient(element));
-      logger.severe(error);
+      logger.severe(e, error);
     }
     return DepositFragment.create(type, xml, error);
   }