Set cros command description properly.

Currently we are incorrectly setting the 'help' field during
ArgumentParser construction, when we should be setting the 'description'
field.

BUG=None
TEST=Unit tests.

Change-Id: I4ceb8525890afd7e98096b97195cff0d04addc92
Reviewed-on: https://gerrit.chromium.org/gerrit/42260
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Ryan Cui <rcui@chromium.org>
Commit-Queue: Ryan Cui <rcui@chromium.org>
diff --git a/scripts/cros.py b/scripts/cros.py
index 2d29061..b2b22f0 100644
--- a/scripts/cros.py
+++ b/scripts/cros.py
@@ -16,7 +16,7 @@
   for cmd_name, class_def in sorted(my_commands.iteritems(), key=lambda x:x[0]):
     epilog = getattr(class_def, 'EPILOG', None)
     sub_parser = subparsers.add_parser(
-        cmd_name, help=class_def.__doc__, epilog=epilog,
+        cmd_name, description=class_def.__doc__, epilog=epilog,
         formatter_class=commandline.argparse.RawDescriptionHelpFormatter)
     class_def.AddParser(sub_parser)