[devtools] fix race when creating backupdir If somebody else creates backupdir between our stat() and mkdir() (like, say, another test running in parallel), we shouldn't crash.

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