migration: Add validate-uuid capability

This capability realizes simple source validation by UUID.
It's useful for live migration between hosts.

Signed-off-by: Yury Kotov <yury-kotov@yandex-team.ru>
Message-Id: <20190903162246.18524-2-yury-kotov@yandex-team.ru>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>