[ctl] Load available configurations in "cubicweb-ctl list" Otherwise we rely on associated ctl plugins to be loaded which is arguably orthogonal to configurations.

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