[recipes.py] add missing helpstrings, merge test subcommands into main parser.

recipe_engine/fetch.py

-# Copyright 2016 The LUCI Authors. All rights reserved.
+# 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.
 
 import calendar
 import httplib
 import json
 import logging
 import os
 import re
 import shutil
@@ skipping 576 matching lines @@
     return CommitMetadata(
       revision,
       rev_json.author_email,
       rev_json.commit_timestamp,
       rev_json.message_lines,
       spec,
       has_interesting_changes(spec, rev_json.changed_files))
 
 
 def add_subparser(parser):
+  helpstr = 'Fetch and update dependencies but take no other action.'
+
   fetch_p = parser.add_parser(
-    'fetch',
-    description='Fetch and update dependencies.')
+    'fetch', help=helpstr, description=helpstr)
 
   def postprocess_func(parser, args):
     if args.no_fetch:
       parser.error('--no-fetch doesn\'t make sense with fetch command')
 
   fetch_p.set_defaults(
     command='fetch',
     # fetch action is implied by recipes.py
     func=(lambda package_deps, engine_flags: 0),
     postprocess_func=postprocess_func,
   )