Ticket 47747 - Add topology fixtures module
    
    Description: Add three topology fixtures in lib389/topologies.py.
    
    It contains:
    - topology_st - with topology_st.standalone inst;
    - topology_m2 and topology_m4 - with dicts
    topology_mN.ms["masterX"]
    topology_mN.ms["masterX_agmts"]["mX_mY"]
    
    To use it in our test we must import the module from lib389
    and use it as a usual fixture afterwards.
    Also, with a new structure we can easily run through masters
    and agreements in loops.
    
    https://fedorahosted.org/389/ticket/47747
    
    Reviewed by: tbordaz, wibrown (Thanks!)