[entities] Move CWSource update_config method as a function in 3.15 migration script This script is the only caller of this method. In the code of the function, drop "skip_unknown" argument and continue accordingly upon OptionError.

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