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/CreateRegistrarGroupsCommand.java

@@ -73,6 +73,15 @@ public class CreateRegistrarGroupsCommand extends ConfirmingCommand
           }})));
   }
 
+  /** Calls the server endpoint to create groups for the specified registrar client id. */
+  static void executeOnServer(Connection connection, String clientIdentifier) throws IOException {
+    connection.send(
+        CreateGroupsAction.PATH,
+        ImmutableMap.of(CreateGroupsAction.CLIENT_ID_PARAM, clientIdentifier),
+        MediaType.PLAIN_TEXT_UTF_8,
+        new byte[0]);
+  }
+
   @Override
   protected String execute() throws IOException {
     for (Registrar registrar : registrars) {