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!)