Fix broken flake8 configuration and flake8 errors which were hidden by this breakage. flake8 --filename options doesn't work as expected: * it's expected to be a shell pattern, using stdlib's fnmatch.fnmatch function internally. This funciton thinks that 'cubicweb/x.py' doesn't match 'cubicweb/x.py' (there must be a reason but that's not the point), hence no file was actually checked ; * as this is a list of pattern, each encountered file is checked against each pattern, leading to run time explosion. So maintain list of files to check in a separated file and give this list to flake8 using unix's xarg command.

#!/bin/sh -e

if [ "$1" = "remove" ]; then
        update-rc.d cubicweb remove >/dev/null
fi
 
if [ "$1" = "purge" ] ; then
        rm -rf /etc/cubicweb.d/
        rm -rf /var/log/cubicweb/
        rm -rf /var/lib/cubicweb/
fi

#DEBHELPER#
 
exit 0