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

recipe_engine/run.py

 # Copyright 2017 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.
 
 """Entry point for fully-annotated builds.
 
 This script is part of the effort to move all builds to annotator-based
 systems. Any builder configured to use the AnnotatorFactory.BaseFactory()
 found in scripts/master/factory/annotator_factory.py executes a single
 AddAnnotatedScript step. That step (found in annotator_commands.py) calls
@@ skipping 500 matching lines @@
     help='The recipe to execute')
   run_p.add_argument(
     'props',
     nargs=argparse.REMAINDER,
     type=parse_prop,
     help=(
       'A list of property pairs; e.g. mastername=chromium.linux '
       'issue=12345. The property value will be decoded as JSON, but if '
       'this decoding fails the value will be interpreted as a string.'))
 
-  run_p.set_defaults(command='run', properties={}, func=main)
+  run_p.set_defaults(properties={}, func=main)
 
 
 def handle_recipe_return(recipe_result, result_filename, stream_engine,
                          engine_flags):
   if engine_flags and engine_flags.use_result_proto:
     return new_handle_recipe_return(
         recipe_result, result_filename, stream_engine)
 
   if 'recipe_result' in recipe_result.result:
     result_string = json.dumps(
@@ skipping 187 matching lines @@
       ret = run_steps(
           properties, stream_engine,
           step_runner.SubprocessStepRunner(stream_engine, engine_flags),
           universe_view, engine_flags=engine_flags,
           emit_initial_properties=emit_initial_properties)
     finally:
       os.chdir(old_cwd)
 
     return handle_recipe_return(
         ret, args.output_result_json, stream_engine, engine_flags)