Is your feature request related to a problem? Please describe.

Currently fileblob sets the permissions to 0777:

We use fileblob to store backups, and we'd prefer this not be world-readable. We'd like to lock this down and use perm.PrivateDir or 0700. It'd be nice to make that the default or make it configurable.

For now, we'll just use os.MkdirAll ourselves.