Bug#873012: not working live migration in qemu ( vm's block storage is LVM )

[Michael Schulz]

However, it's not necessary to have the vm block storage device on an LVM 
logical volume; live migration with --copy-storage-all also got stuck (as 
described above) when vm block storage is a qcow2 file on both sides.

Tested on 1:2.8+dfsg-6+deb9u2