Automatically create mailing lists for registrars

This improves one of our gTech processes so they no longer have to remember to create Google Groups for a registrar after creating that registrar.

The ConfirmingCommand.verify() method is renamed to be more general purpose, so that it can do anything that follows naturally after a successful execution, such as creating Google Groups groups.

Minor refactoring is done around RegistryToolEnvironment handling for tests to make it more bullet-proof and general case.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=117494277

java/com/google/domain/registry/tools/AllocateDomainCommand.java

@@ -68,7 +68,7 @@ final class AllocateDomainCommand extends MutatingEppToolCommand {
   private final List<Key<DomainApplication>> applicationKeys = new ArrayList<>();
 
   @Override
-  protected String verify() throws Exception {
+  protected String postExecute() throws Exception {
     StringBuilder builder = new StringBuilder();
     // Check to see that we allocated everything.
     return builder.append(ofy().transactNewReadOnly(new Work<String>() {