[tox] Drop "exclude" option from flake8 config and adjust flake8-ok-files.txt accordingly Some files listed in flake8-ok-files.txt were excluded of flake8 run because of the "exclude" option in tox.ini. Some of them were non-existent files (moved), some others were actually non-flake8-compliant. In the latter case, we adjust trivial errors (blank lines, module import not on top of file) but remove others (like cubicweb/test/unittest_utils.py) from flake8-ok-files.txt.

^build$
^dist$
\.egg-info$
^.tox$
^.cache$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
\.pybuild
debian/python-cubicweb
debian/*.log
debian/*.substvars
debian/cubicweb-doc
debian/cubicweb
debian/files

syntax: regexp
.*/data.*/database/.*
.*/data/ldapdb/.*
.*/data/uicache/
.*/data/libpython/cubicweb_.*/i18n/.*\.po
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
^doc/_build
^doc/js_api/
test-results.xml