Leaking Permissions

[eriq-augustine]

In most driver-level operations, we leak some information that the caller should not be privy to.
For example, when we make a dir we will first check to see if the parent directory exists and then we will check if we have permission to write there.
If the context user does not have read permissions on the parent directory, then they now have the additional information that the directory exists.

We do this so that we can return more clear errors.