Export entity integrity alerts to BigQuery

This is part 2 of a longer series.  Part 3 will add lots more tests, will add a cron entry, and will include an analysis script to run on BigQuery to detect the presence of two consecutive errors.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=120040267

javatests/com/google/domain/registry/testing/DatastoreHelper.java

@@ -46,6 +46,7 @@ import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.ImmutableSortedMap;
 import com.google.common.collect.Iterables;
 import com.google.domain.registry.config.RegistryEnvironment;
+import com.google.domain.registry.model.Buildable;
 import com.google.domain.registry.model.EppResource;
 import com.google.domain.registry.model.EppResource.ForeignKeyedEppResource;
 import com.google.domain.registry.model.ImmutableObject;
@@ -710,6 +711,9 @@ public class DatastoreHelper {
   }
 
   private static <R> R persistResource(final R resource, final boolean wantBackup) {
+    assertWithMessage("Attempting to persist a Builder is almost certainly an error in test code")
+        .that(resource)
+        .isNotInstanceOf(Buildable.Builder.class);
     ofy().transact(new VoidWork() {
       @Override
       public void vrun() {