Existing code
```
{
if os.IsNotExist(e) {
e = os.MkdirAll(objectDir, 0700)
if e != nil {
return "", probe.NewError(e)
}
}
return "", probe.NewError(e) ---> Error was here.
}
```
For a successful 'MkdirAll' it would still return an empty uploadID,
but the 'error' would be nil. This would succeed the request but
client would fail.
Fix is to re-arrange the logic. Thanks to Alexander Neumann @fd0, for
reporting this problem.
- limit list buckets to limit only 100 buckets, all uppercase buckets
are now lowercase and work transparently with all calls.
- Change disk.Stat to disk.GetInfo and return back disk.Info{} struct.
- Introduce new ioutils package which implements ReadDirN(path, n),
ReadDirNamesN(path, n)
