use pyftpdlib logging and let it deal with unicode issues
Fixed broken tests

Tests were broken in aa202fa8e89910decf80eed050caf1ba373d9662 and in consequence
the unicode support testing was wrong.

fs input is expected to be unicode, ftp tests were correct.
Unicode fixes

- error translation may include unicode
- unicode support for keys in shared cache
- cache search is always string based
- fix for list dir and list dir with stats