[cubicweb-ctl] move to accepting only once instance name per command The rationals behind this decision are: - while in the past managing all instances sytem wide made a lot of sens, pratices have evolved today and we've moved to managing one instance by one - this makes things easier to debug since commands since using them on several instances were making this harder (errors hidden in the middle) - also solve the problem of the return code to have, before it was always 0 which prevented to do things like: ipython --pdb $(which cubicweb-ctl) $command $instance or shell scripts that used it - this simplify the code and is always good to take

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