utils/get-developers: use parser.error() rather than canned print+return

parser.error() reports a nice error message, that also displays a short
reminder of the available options.

Adapt the test-suite accordingly: previously, the error string was an
exact string in the stdout list, while it now is a substring in one of
the strings in stderr. The exit code changes, too.

Signed-off-by: Yann E. MORIN <yann.morin@orange.com>
Cc: Julien Olivain <ju.o@free.fr>
Signed-off-by: Julien Olivain <ju.o@free.fr>

utils/get-developers

@@ -40,11 +40,9 @@ def __main__():
     if len(args.patches) != 0:
         action += 1
     if action > 1:
-        print("Cannot do more than one action")
-        return
+        parser.error("Cannot do more than one action")
     if action == 0:
-        print("No action specified")
-        return
+        parser.error("No action specified")
 
     devs = getdeveloperlib.parse_developers(args.filename)
     if devs is None: