Ticket 47828: DNA scope: allow to exlude some subtrees
    
    Bug Description:
    	DNA plugin generates attributes values to any added entry
    	in the scope of the plugin (and filter).
    	For ULC (http://www.freeipa.org/page/V3/User_Life-Cycle_Management),
    	the provisioning container must be excluded.
    
    Fix Description:
    	Add the ability to define multivalued attribute: "dnaExcludeScope"
    	in the config entry.
    	DNA will not generate attributes values for entries added
    	under one of the excluded DIT
    
    http://fedorahosted.org/389/ticket/47828ticket URL>
    
    Platforms tested: F17/F20
    
    Reviewed by : Noriko (many thanks)
    
    Flag Day: no
    
    Doc impact: yes (adding a config attribute)