[sheepdog] Add confirm before format cluster

[Liu Yuan]

On 12/13/2012 12:09 AM, Valerio Pachera wrote:
> Hi, I suggest to add a message before format the cluster (at least if
> it contains any vdi).
> 
> ---
> collie vdi create test 1G
> collie vdi list
>   Name        Id    Size    Used  Shared    Creation time   VDI id  Copies  Tag
>   test         1  1.0 GB  0.0 MB  0.0 MB 2012-12-12 17:00   7c2b25
> 2
> collie cluster format
>   using backend farm store
> ---
> 
> This just to avoid a mistake that can be done if working late and being tired:
> instead of typing the harmless
>   'collie cluster info'
> type
>   'collie cluster format'
> 
> ...and loose everything!
> 

I have pushed the patch to the master and now you'll be warned by a nice
dog if the cluster isn't empty.

Thanks,
Yuan