examples: python: print into stderr

https://mail.gnome.org/archives/networkmanager-list/2015-March/msg00024.html

Signed-off-by: Petr Vorel <petr.vorel@gmail.com>

examples/python/gi/firewall-zone.py

@@ -75,5 +75,5 @@ if __name__ == "__main__":
                 print("'%s' zone set to '%s'") % (c.get_id(), new_zone)
             break
     if not found:
-        print ("Error: connection '%s' not found.") % (con_name)
+        sys.stderr.write("Error: connection '%s' not found.\n") % (con_name)
         main_loop.quit()