EIO createDirectoryRecursively() errors if it exists

[Nadyita]

When I'm using the EIO driver, calling yield filesystem()->createDirectoryRecursively("/tmp"); errors out, while the BlockingDriver returns new Success(). It would be nice if they behave identical, so we don't have to wrap our calls in exists-checks.

On a related note, it took me very long to find this error, because the EIO error-messages seem to get mixed up. The actual error I got was 'No such file or directory', but when trying to reproduce the problem, I got the correct 'File exists' error. I will try to find a minimum example to reproduce this.