[test] Add a test ensuring new cube built from skeleton is flake8-compliant
And make skeleton files actually flake8-compliant henceforth.
\.svn
^build$
^dist$
\.egg-info$
^.tox$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
syntax: regexp
.*/data.*/database/.*
.*/data/ldapdb/.*
.*/data/uicache/
.*/data/cubes/.*/i18n/.*\.po
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
^doc/_build
^doc/js_api/