You can clone with
AFAICT, all the syntastic implementation of flake8 return errors and warnings as errors. Flake8's error code starts with an E or W for error or waring. From what I see from the improved pylint changes, it seems that the regex to do this already exists in the pylint syntax checker. Also of use might be vim-flake8's errorformat string.
Or, I could just use pylint with syntastic. Everything works and is awesome!
FWIW, this was addressed here 9504f52