[sheepdog] auto recovery after mount failure

[Dietmar Maurer]

normally people mount sheepdog data disks in fstab. That way the disks 
get mounted at boot. For example, we have the following mounts:

/dev/sda ==> /
/dev/sdb ==> /var/lib/sheepdog

The problem occurs when mounting the sheepdog data disk fails 
at boot time (for example: damaged disk, admin triggered reboot).
In  that case /var/lib/sheepdog is empty (and on /dev/sda).

The boot process continues, and 'sheep' simply creates a new 'farm' 
in /var/lib/sheepdog. Even worse, It immediately start auto-recovery,
which fills the root disk in short time.

Any idea how to prevent that. Maybe we should not create/initialize the 
storage automatically at startup, man used a 'mksheepdogfs' to initialize the dir.
That way the 'sheep' can check if the directory is initialized/mounted?

- Dietmar