[sheepdog] auto recovery after mount failure

[Dietmar Maurer]

> I don't think mkfs tool is necessary for Sheepdog. Sheepdog operate on the
> very high level construct, known as 'directory', so we can play storage tricks
> behind and if any problem could be solved outside Sheepdog, we prefer to
> solve it outside unless it is proved reasonable and necessary to solve it inside
> Sheepdog.

I already pointed out a serious problem with the current behavior, and I just want to fix that. So what fix do
you suggest to avoid those problems?

- Dietmar