Refactor out creation of server TRIDs so they can be tested

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=152837185

javatests/google/registry/testing/EppExceptionSubject.java

@@ -47,7 +47,7 @@ public class EppExceptionSubject extends Subject<EppExceptionSubject, EppExcepti
     try {
       marshal(
           EppOutput.create(new EppResponse.Builder()
-              .setTrid(Trid.create(null))
+              .setTrid(Trid.create(null, "server-trid"))
               .setResult(actual().getResult())
               .build()),
           ValidationMode.STRICT);