The upcoming virDomainBackup() API needs to take advantage of the
ability to expose a bitmap as part of nbd-server-add for a pull-mode
backup (this is the recently-added QEMU_CAPS_NBD_BITMAP capability).
Signed-off-by: NEric Blake <eblake@redhat.com>
Acked-by: NPeter Krempa <pkrempa@redhat.com>