v2v: Update TODO.
v2v: -i libvirtxml: Only handle NBD source with host 'localhost', for virt-p2v.

We only care/support virt-p2v for network disks.  Give a warning about
anything else.

This avoids a potential quoting issue.
v2v: Reduce use of polymorphic variants.

Ordinary variants prevent coding errors.
v2v: adding --vdsm-ovf-output option

This option is needed by vdsm for writing the ovf to a specific directory.
The default is current directory.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1176598
Signed-off-by: Shahar Havivi <shaharh@redhat.com>