New API: add-domain

New API: add-domain

This new API allows you to add the disks from a libvirt
domain.

In guestfish you can use the 'domain' command to access the
API, eg:

><fs> domain Fedora14 libvirturi:qemu:///system
1

The returned number is the number of disks that were added.

Also here is a proposed (but commented out) low-level API
which would allow you to add a domain from a virDomainPtr.
However there are several problems with this API -- see discussion
on the list:
https://www.redhat.com/archives/libguestfs/2010-November/thread.html#00028