ipapwd_extop should use TARGET_DN defined by a pre-extop plugin
    
    ipapwd_extop allows to update the password on a specific entry, identified by its DN.
    It can be usefull to support virtual DN in the extop so that update of a virtual entry
    would land into the proper real entry.
    
    If a pre-extop sets the TARGET_DN, ipapwd_extop sets ORIGINAL_DN with the value
    of TARGET_DN, instead of using the original one (in the ber req)
    There is a dependency on slapi-nis >= 0.56-0.1 (https://fedorahosted.org/freeipa/ticket/5955)
    
    https://fedorahosted.org/freeipa/ticket/5946
    
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>