[sheepdog] read/write during recovery

[Dietmar Maurer]

>IIUC, your patch does not handle write requests because write
>journaling is not implemented yet, yes?  I think it is not easy to
>implement journaling across nodes.  Do you have any ideas to
>implement it simply?

The current code simply queues all request in RAM (wait_obj_queue).
Instead, I thought we can use the code from journal.c, but create
journals inside object specific recovery directory:

/path/to/farm/recovery/obj/

If we use that, we can answer wit SUCCESS to write request immediately.
And we use less memory.

- Dietmar