devtool: add: allow specifying URL as positional argument

Having to specify -f is a little bit ugly when a URI is distinctive
enough to recognise amongst the other positional parameters, so take it
as an optional positional parameter. -f/--fetch is still supported, but
deprecated.

(From OE-Core rev: aedfc5a5db1c4b2b80a36147c9a13b31764d91dd)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/devtool

@@ -280,6 +280,8 @@ def main():
         if str(err):
             logger.error(str(err))
         ret = 1
+    except argparse_oe.ArgumentUsageError as ae:
+        parser.error_subcommand(ae.message, ae.subcommand)
 
     return ret