DP: Reorganize memory hierarchy of requests
    
    This function alters the memory hierarchy of the be_req
    to ensure memory safety during shutdown. It creates a
    spy on the be_cli object so that it will free the be_req
    if the client is freed.
    
    It is generally allocated atop the private data context
    for the appropriate back-end against which it is being
    filed.
    
    https://fedorahosted.org/sssd/ticket/1226