fish: Reimplement -i option using new C-based inspection.

fish: Reimplement -i option using new C-based inspection.

Don't shell out to virt-inspector.  Instead, use the new C-based
inspection APIs.

This is much faster.

The new syntax is slightly different:

  guestfish -a disk.img -i
  guestfish -d guest -i

However, the old syntax still works.