Ticket 47595 - fail to detect/reinit already existing instance/backup
    
    Bug Description:
    	We need to re-initialize an instance from a previously taken backup.
    	lib389 had not the capability to test if an instance existed and a backup existed.
    
    Fix Description:
    	Fix for backup/restore:
    		- before restore clean up
    			DB directory from previous '.db' files and backend dirs
    			errors/access log files
    	Testing existance of backup/instance
    		- support offline dirsrv instance for offline access
    		- add checkInstance/_offlineDirsrv/existsBackup/existsInstance
    		- fix clearInstanceBackupFS
    	Misc:
    		- fix backup/restore functions (replica.changelog, instanceBackupFS, instanceRestoreFS)
    
    https://fedorahosted.org/389/ticket/47595
    
    Reviewed by: Rich Megginson
    
    Platforms tested: Fedora 19 (jenkins)
    
    Flag Day: no
    
    Doc impact: no