clean-up and adjustments also related with OOIION-1352 and OOIION-1495.

- capture instrument_ids associated with ports in auxiliary PortNode objects;
- for tests, always load network definition directly from yaml, not via RSN OMS (this was already done for mission manager tests, but now it's the default in the base test class)
- remove unneeded supporting class and test after these changes.
Merge pull request #2165 from carueda/pa_config_and_oms

clean-up and adjustments also related with OOIION-1352 and OOIION-1495.