Add --noinstantiate to qmlplugindump

This flag allows you to run qmlplugindump on plugins which cannot safely
create objects, such as plugins with unusual requirements or missing
essential dependencies.

Change-Id: Ifcc542b8dec5358fc8a76d78a2a272c9cbf5d78a
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>