theia: support moving file on different filesystem during resiliency export
Due to disk usage on my production server, I had to move the theia's backup to a different file system. I bind mount this other fs on: slappart0/srv/backup/theia Mounting on "slappart0/srv/backup" would make logrogate complain (logrotate is used in the "backup" cron, triggering the resiliency process). So "slappart0/srv/backup/theia" was the 2nd best idea. Unfortunately for my case, os.rename raises if the src and dest filesystems are different, as it os.rename guarantees the atomicity of the operation. As atomicity is not that important for copying the signature file, it can be replaced by shutil.move.