block: List anonymous device BBs in query-block

block: List anonymous device BBs in query-block

Instead of listing only monitor-owned BlockBackends in query-block, also
add those anonymous BlockBackends that are owned by a qdev device and as
such under the control of the user.

This allows using query-block to inspect BlockBackends for the modern
configuration syntax with -blockdev and -device.

Signed-off-by: Kevin Wolf <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
Reviewed-by: John Snow <[email protected]>