Update prebuilt.py to ignore invalid arguments to workaround cbuild bugs.

cbuild passes in invalid arguments on this branch. On trunk we have already
switched away from cbuild so there is no need to ignore invalid arguments.
But this change is needed as a workaround on the branch.

TEST=Test prebuilt.py ignores invalid arguments.

Change-Id: Ice879dd8088c2de5a5b1b5845fa801b6bd02d5ba
Reviewed-on: http://gerrit.chromium.org/gerrit/3758
Reviewed-by: Jay Kim <yongjaek@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: David James <davidjames@chromium.org>
diff --git a/buildbot/prebuilt.py b/buildbot/prebuilt.py
index 2b874a6..c701868 100755
--- a/buildbot/prebuilt.py
+++ b/buildbot/prebuilt.py
@@ -649,9 +649,6 @@
     usage(parser, 'Error: you need provide a chroot path')
   if not options.upload:
     usage(parser, 'Error: you need to provide an upload location using -u')
-  if args:
-    usage(parser, 'Error: invalid arguments passed to prebuilt.py: %r' % args)
   if options.upload_board_tarball and not options.upload.startswith('gs://'):
     usage(parser, 'Error: --upload-board-tarball only works with gs:// URLs.\n'