Support for qcow2 block images

[dann1]

Using qemu-nbd kernel module, we could mount qcow2 blocks on the container directory.

The module is loaded issuing

apt install qemu-utlis
modprobe nbd

This is an example of mapping an image file into a block device
qemu-nbd -c /dev/nbd0 /var/lib/vz/images/107/vm-107-disk-1.qcow2

Then we could mount it as a regular volume.

To unmap the image file
qemu-nbd -d /dev/nbd0