[style] Make toolsutils.py flake8-clean Run `autopep8 --max-line-length 100 -i cubicweb/toolsutils.py` and fixed unused imports.

[test/rset] typo

[test/rset] flake8

[py3] import configparser from six.moves instead of using a try/except Using six is better than the try/except because it clearly indicates compatibility code. Also, when using tools such as vermin which relies on AST, it helps getting rid of false compatibility errors.