add live storage migration with vm migration

add live storage migration with vm migration

This allow to migrate disks on local storage  to a remote node storage.

When the target node start, a new volumes are created and exposed through qemu embedded nbd server.

qemu drive-mirror is launch on source vm for each disk with nbd server as target.

when drive-mirror reach 100% of 1 disk, we don't complete the block jobs and begin mirror of next disk.
(mirroring are parralel, but we try to mirroring them 1 by 1 to avoid storage && network overload)

Then we live migrate the vm to destination node. (drive-mirror still occur at the same time).

We the vm is livemigrate (source vm paused, target vm pause), we complete the block jobs mirror.

When is done we stop the source vm and resume the target vm

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>