Add short option for --bot in submit_try

tools/submit_try

 #!/usr/bin/python
 
 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 
 """
 submit_try: Submit a try request.
 
@@ skipping 130 matching lines @@
       return self._changelist
 
     @property
     def revision(self):
       return self._revision
 
   usage = (
 """submit_try: Submit a try request.
 submit_try %s--bot <buildername> [<buildername> ...]
 
---bot               Builder on which to run the try. Required.
+-b, --bot           Builder on which to run the try. Required.
 -h, --help          Show this message.
 -r <revision#>      Revision from which to run the try.
 -l, --list_bots     List the available try builders and exit.
 """ % ('<changelist> ' if is_svn else ''))
 
   def Error(msg=None):
     if msg:
       print msg
     print usage
     sys.exit(1)
 
   using_bots = None
   changelist = None
   revision = None
 
   while argv:
     arg = argv.pop(0)
     if arg == '-h' or arg == '--help':
       Error()
     elif arg == '-l' or arg == '--list_bots':
       print 'submit_try: Available builders:\n  %s' % '\n  '.join(trybots)
       sys.exit(0)
-    elif arg == '--bot':
+    elif arg == '-b' or arg == '--bot':
       if using_bots:
         Error('--bot specified multiple times.')
       if len(argv) < 1:
         Error('You must specify a builder with "--bot".')
       using_bots = []
       while argv and not argv[0].startswith('-'):
         bot = argv.pop(0)
         if bot == ALL_BUILDERS:
           if using_bots:
             Error('Cannot specify "all" with additional builder names.')
@@ skipping 70 matching lines @@
 
   # Parse and validate the command-line arguments.
   args = ValidateArgs(sys.argv[1:], trybots=trybots, is_svn=is_svn)
 
   # Submit the try request.
   SubmitTryRequest(args, is_svn=is_svn)
 
 
 if __name__ == '__main__':
   sys.exit(main())