With -blockdev qemu will not report any useful "device" for the data
returned by 'query-block'. We need to start using the 'qdev' field to do
so in cases when "device" is empty or it does not match the entry name.

This patch adds data for the 'qdev' field into the returned data
structure.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>