Issue 83 - Add an util for generating instance parameters
    
    Description: Currently, we create instance parameters (HOST_MASTER_1,
    PORT_MASTER_1, etc.) in _constants.py module.
    The commit adds generate_ds_params() to lib389.utils.
    
    The util can generate a host, port, secure port, server ID and replica ID
    for the selected role and instance number. I.e. inst_num=1, role="master".
    
    Fix topologies.py module to use the new util.
    Add create_topology() function.
    Remove agmts from TopologyMain, we should use agreement module for that.
    
    https://pagure.io/lib389/issue/83
    
    Reviewed by: wibrown (Thanks!)