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

[py3] Decode subprocess stdout in toolsutils.show_diffs() On Python 3, subprocess' pipes are bytes stream so we must decode them before printing. Without this change, diff of configuration files (e.g. all-in-one.conf as displayed upon instance upgrade) will rendered as a single line on Python 3.

[python3] make sure staticcontroller returns a bytes instance The ``publish()`` method of controller is supposed to return a bytes intsance. Returning a text_type instance will crash later on in the Pyramid response handler when assigning content to ``response.body`` (at least in Python3):: >>> from pyramid.response import Response >>> r = Response() >>> r.body = '' Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/adim/.virtualenvs/…/response.py", line 562, in _body__set raise TypeError(msg) TypeError: You cannot set Response.body to a text object (use Response.text)