[recipes.py] use argparse to set command automatically.

recipe_engine/autoroll.py

 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 from __future__ import print_function
 
 import copy
 import json
 import logging
 import os
@@ skipping 275 matching lines @@
           'Requires --output-json.'))
 
   def postprocess_func(parser, args):
     if args.no_fetch:
       parser.error('autoroll with --no-fetch does not make sense.')
 
     if args.verbose_json and not args.output_json:
       parser.error('--verbose-json passed without --output-json')
 
   autoroll_p.set_defaults(
-    command='autoroll', func=main, postprocess_func=postprocess_func)
+    func=main, postprocess_func=postprocess_func)
 
 
 def main(_package_deps, args):
   config_file = args.package
   repo_root = package.InfraRepoConfig().from_recipes_cfg(config_file.path)
 
   package_pb = config_file.read()
 
   context = package.PackageContext.from_package_pb(
     repo_root, package_pb, allow_fetch=not args.no_fetch)
@@ skipping 12 matching lines @@
       # Restore initial state. Since we could be running simulation tests
       # on other revisions, re-run them now as well.
       write_spec_to_disk(context, repo_cfg_block, config_file, package_pb)
       run_simulation_test(repo_root, package_spec.recipes_path, ['train'])
 
   if args.output_json:
     with args.output_json:
       json.dump(results, args.output_json, sort_keys=True, indent=2)
 
   return 0