[pkg] require python >= 3.4 This avoid pip pulling a version that does not run on python2 when using a python2 environment. Since we already released some 3.27 releases in pypi, I think we should release 3.27.3 and remove releases 3.27.2, 3.27.1 and 3.27.0 from pypi.

etc/init.d
etc/cubicweb.d
usr/bin
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances