Use pkgutil.ImpLoader instead of a custom loader for cubes import redirection It just works fine (same implementation of load_module method as _CubesLoader introduced in d404fd8499dd) and is complete w.r.t. PEP 302 (all methods implemented). Related to #13001466.

etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances