[libvirt] Expose qemu monitor command query_block?

Command "query-block" is only used internally for medium's checking before migration currently. Should we expose it as a public API, such as virDomainQueryBlock (or a qemu specific API, virDomainQemuQueryBlock)? It has enough useful infomation which user may care out, such as "io-status", "locked", "removable", "inserted". And perhaps more info in future. Osier