[Libguestfs] example script for GObject

I tried using Javascript (gjs) with GObject-Introspection and did a port of the create_disk example which is attached below. Quite a bit of time was spent looking up stuff in the GLib reference and guessing how certain idioms translate to gjs. I used the traditional add_drive_opts method since I haven't been able to find how to specify the optional arguments to add_drive_opts. How does that work? Cheers, -Hilko