This review differs from previous with:
* skip verbose option (use of log.level).
* use glob.glob to retrieve files matching rather that os.walk
* fix a bug in instanceBackupFS that did not return an already
existing backup
* add two functions to handle instance backup: clearInstanceBackupFS
(to remove one or all backups of an instance), _infoInstanceBackupFS
(just to keep path/pattern info of backup into a single routine)
https://fedorahosted.org/389/attachment/ticket/47584/0003-Ticket-47584-CI...