Add Client-side OAuth2 to HTTP connections

Implement client-side OAuth in non-local HTTP connections.  Also add tests to
verify that the different modes of connection are set up correctly.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=147636222

java/google/registry/tools/RegistryToolComponent.java

@@ -43,6 +43,8 @@ import javax.inject.Singleton;
     DatastoreServiceModule.class,
     CloudDnsWriterModule.class,
     DefaultRequestFactoryModule.class,
+    DefaultRequestFactoryModule.AuthorizerModule.class,
+    DefaultRequestFactoryModule.DataStoreFactoryModule.class,
     DefaultRequestFactoryModule.RequestFactoryModule.class,
     DnsUpdateWriterModule.class,
     DummyKeyringModule.class,