Make failfastForCreate for domain and application creates explicitly hit memcache

TESTED=For all tests, I added @Cache to DomainBase because otherwise the tests will
    fail. We aren't ready to do this in prod yet, which is why the tests are still
    marked @Ignore. The new tests fail if you change line 134 in Ofy to not use memcache
    and either use the unchanged original DomainCreateFlow code, or use the new
    inlined code and change loadWithMemcache() to load(). They pass with the new
    inlined code that calls loadWithMemcache(), as long as the @Cache is added to
    DomainResource.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=154224748

java/google/registry/model/index/ForeignKeyIndex.java

@@ -62,7 +62,7 @@ public abstract class ForeignKeyIndex<E extends EppResource> extends BackupGroup
   @Entity
   public static class ForeignKeyHostIndex extends ForeignKeyIndex<HostResource> {}
 
-  private static final ImmutableMap<
+  static final ImmutableMap<
           Class<? extends EppResource>, Class<? extends ForeignKeyIndex<?>>>
       RESOURCE_CLASS_TO_FKI_CLASS =
           ImmutableMap.<Class<? extends EppResource>, Class<? extends ForeignKeyIndex<?>>>of(
@@ -102,14 +102,19 @@ public abstract class ForeignKeyIndex<E extends EppResource> extends BackupGroup
     return topReference;
   }
 
-  /**
-   * Create a {@link ForeignKeyIndex} instance for a resource, expiring at a specified time.
-   */
+
+  @SuppressWarnings("unchecked")
+  public static <T extends EppResource> Class<ForeignKeyIndex<T>> mapToFkiClass(
+      Class<T> resourceClass) {
+    return (Class<ForeignKeyIndex<T>>) RESOURCE_CLASS_TO_FKI_CLASS.get(resourceClass);
+  }
+
+  /** Create a {@link ForeignKeyIndex} instance for a resource, expiring at a specified time. */
   public static <E extends EppResource> ForeignKeyIndex<E> create(
       E resource, DateTime deletionTime) {
     @SuppressWarnings("unchecked")
-    Class<? extends ForeignKeyIndex<E>> fkiClass =
-        (Class<? extends ForeignKeyIndex<E>>) RESOURCE_CLASS_TO_FKI_CLASS.get(resource.getClass());
+    Class<ForeignKeyIndex<E>> fkiClass =
+        ForeignKeyIndex.mapToFkiClass((Class<E>) resource.getClass());
     ForeignKeyIndex<E> instance = instantiate(fkiClass);
     instance.topReference = Key.create(resource);
     instance.foreignKey = resource.getForeignKey();
@@ -120,7 +125,7 @@ public abstract class ForeignKeyIndex<E extends EppResource> extends BackupGroup
   /** Create a {@link ForeignKeyIndex} key for a resource. */
   public static Key<ForeignKeyIndex<?>> createKey(EppResource resource) {
     return Key.<ForeignKeyIndex<?>>create(
-        RESOURCE_CLASS_TO_FKI_CLASS.get(resource.getClass()), resource.getForeignKey());
+        mapToFkiClass(resource.getClass()), resource.getForeignKey());
   }
 
   /**
@@ -162,11 +167,10 @@ public abstract class ForeignKeyIndex<E extends EppResource> extends BackupGroup
    * <p>The returned map will omit any keys for which the {@link ForeignKeyIndex} doesn't exist or
    * has been soft deleted.
    */
-  @SuppressWarnings("unchecked")
   public static <E extends EppResource> Map<String, ForeignKeyIndex<E>> load(
       Class<E> clazz, Iterable<String> foreignKeys, final DateTime now) {
-    return (Map<String, ForeignKeyIndex<E>>) filterValues(
-        ofy().load().type(RESOURCE_CLASS_TO_FKI_CLASS.get(clazz)).ids(foreignKeys),
+    return filterValues(
+        ofy().load().type(mapToFkiClass(clazz)).ids(foreignKeys),
         new Predicate<ForeignKeyIndex<?>>() {
           @Override
           public boolean apply(ForeignKeyIndex<?> fki) {