some safety dances

  - make a backup in a temporary direcotry and move it to the
    appropriate place when succesfully finished
  - on restore innobackupex (xtrabackup) changes / writes to the
    incremental backup direcotries. to avoid this the incremental
    backup directory gets copied to a temporary path. from there,
    the restore process is started and the temporary direcotry gets
    removed. needs more place ...