Live migration for Libvirt vz driver works the same
way as for qemu. However some migration capabilities
are supported differently:
* Virtuozzo containers doesn't use backing file, so
we shouldn't ensure it exists in pre live migration.
* migrate_disks parameter doesn't make sense for
Virtuozzo, as backend determines whether specific
block device should be migrated or not.
* Passing new domain xml to migration method is not
supported.
Implements: blueprint live-migration-vz-driver
Change-Id: I89ecdef13ad47800abc8a5158f8834e46750b9ea
Signed-off-by: Pavel Gluschak <pglushchak@virtuozzo.com>