qemu-doc: Add UUID support in initiator name

Update doc with the usage of UUID for initiator name.

Related-To: https://bugzilla.redhat.com/1006468
Signed-off-by: Fred Rolland <frolland@redhat.com>
Message-id: 20170823084830.30500-1-frolland@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
