storage: Fix volume cloning for logical volume.
storage: Fix volume cloning for logical volume.

https://bugzilla.redhat.com/show_bug.cgi?id=948678

When creating a logical volume with virStorageVolCreateXMLFrom,
"qemu-img convert" is called internally if clonevol is a file volume.
Then, vol->target.format is used as output_fmt parameter but the
target.format of logical volumes is always 0 because logical volumes
haven't the volume format type element.

Fortunately, 0 was treated as RAW file format before commit f772b3d9,
so there was no problem. But now, 0 is treated as the type of none,
qemu-img fails with "Unknown file format 'none'".

This patch fixes this issue by treating output block devices as RAW
file format like for input block devices.

Signed-off-by: Atsushi Kumagai <39d7451d585f773af30891a53feb06e85def8e7d@mxc.nes.nec.co.jp>
(cherry picked from commit d369e50825b88251d13a489efa2a58919b18a2c2)

mithleshvrts/libvirt-0.10.2,mithleshvrts/libvirt-0.10.2,mithleshvrts/libvirt-0.10.2,mithleshvrts/libvirt-0.10.2,mithleshvrts/libvirt-0.10.2