migrate: add live-migration of replicated disks

migrate: add live-migration of replicated disks

with incremental drive-mirror and dirty-bitmap tracking.

1.) get replicated disks that are currently referenced by running VM
2.) add a block-dirty-bitmap to each of them
3.) replicate ALL replicated disks
4.) pass bitmaps from 2) to drive-mirror for disks from 1)
5.) skip replicated disks when cleaning up volumes on either source or
target

added error handling is just removing the bitmaps if an error occurs at
any point after 2, except when the handover to the target node has
already happened, since the bitmaps are cleaned up together with the
source VM in that case.

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Tested-by: Stefan Reiter <s.reiter@proxmox.com>