tests: Allow Tracker.dn be an instance of Fuzzy
    
    Some of the IPA LDAP entries are using ipaUniqueID as
    the "primary key". To match this UUID based attribute
    in assert_deepequal, an instance of Fuzzy class must
    be used. This change adds the possibility to assign
    the Fuzzy object as the DN for the tracked entry.
    
    The user may need to override the rdn and name
    properties for the class using the Fuzzy DN.
    
    Reviewed-By: Lenka Doudova <ldoudova@redhat.com>