Concurrent transaction issue

With latest Argon upstream dependencies, tapi/test03_tapi_device_change_notifications functional test fails almost all the time.

It seems there is a strong concurency issue between read and write transactions initiated by openroadm topology update thread and tapi topology update thread. One need to access to the configuration datastore, whereas the other to the operational one, and the different transactions initiated by the two thread in parallel are not correctly managed.

Need to review the RequestProcessor implementation to solve that.