Ticket 47449 - deadlock after adding and deleting entries
    
    Bug Description:  If multiple clients are each doing their own add/delete of the same entries,
                      the server will deadlock very quickly.
    
    Fix Description:  The server was not signaling an error when it failed to lock the parent
                      entry lock.  I've checked add/mod/modrdn functions as well, and they do correctly
                      unlock the cache entry(this includes the old/new superior for modrdn).
    
    https://fedorahosted.org/389/ticket/47449
    
    Reviewed by: richm(Thanks!)
    (cherry picked from commit 66fbebc7d4c6552fcbbea7351dea5527d88195a1)