This makes the blkdebug suspend/resume functionality available in
qemu-io. Use it like this:

  $ ./qemu-io blkdebug::/tmp/test.qcow2
  qemu-io> break write_aio req_a
  qemu-io> aio_write 0 4k
  qemu-io> blkdebug: Suspended request 'req_a'
  qemu-io> resume req_a
  blkdebug: Resuming request 'req_a'
  qemu-io> wrote 4096/4096 bytes at offset 0
  4 KiB, 1 ops; 0:00:30.71 (133.359788 bytes/sec and 0.0326 ops/sec)

Signed-off-by: Kevin Wolf <kwolf@redhat.com>