[Libvir] Capabilities XML format

[Mark McLoughlin]

Hi,
	One other comment - we should expose how a guest can be booted - i.e.
what values of <boot dev='foo'> is supported and whether <kernel> is
supported.

	e.g. QEMU should be able to boot with a supplied kernel/initrd or, as
Dan points out, over the network using PXE.

Cheers,
Mark.