v2v: If virtio is enabled, map device names to vd* (RHBZ#1142004).

The old virt-v2v code had:

    my $prefix;
    if ($virtio) {
        $prefix = 'vd';
    } elsif ($libata) {
        $prefix = 'sd';
    } else {
        $prefix = 'hd'
    }

The translated code dropped the test for virtio by accident, which
meant that device names would be mapped to sd* or hd* even if the
virtio-blk driver was enabled for the guest.

Thanks: Tingting Zheng
v2v: -o rhev/vdsm: Fix ovf:size and ovf:actual_size fields (RHBZ#1142008).

These are integers in gigabytes (2^30).

Thanks: Shahar Havivi.
v2v: Fix capitalization of ovf:volume-type (RHBZ#1142008).

Thanks: Shahar Havivi.
v2v: Fix OVF VmType field, which should be 0 or 1 (RHBZ#1142008).

Thanks: Shahar Havivi.
v2v: -o rhev: Chown the image files and metadata after the upload.
v2v: -o rhev: Don't quote 'root' in error message.