Refuse to push the attention button in case the guest is busy with some
hotplug operation (as indicated by the power indicator blinking).

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20211111130859.1171890-4-kraxel@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>