eda88c94ed
we format lvm logical volume with qcow2 to handle snapshot chain.
like for qcow2 file, when a snapshot is taken, the current lvm volume
is renamed to snap volname, and a new current lvm volume is created
with the snap volname as backing file
snapshot volname is similar to lvmthin : snap_${volname}_{$snapname}.qcow2
Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>