Fix MockTransportLayerClient for unit tests.

Fixing setup of scheduler client unit tests by adding implementation of
this classmethod, declared as abstract in upstream superclass.

python/lib/communication/dmod/test/test_scheduler_client.py

@@ -9,6 +9,10 @@
 
 class MockTransportLayerClient(TransportLayerClient):
 
+    @classmethod
+    def get_endpoint_protocol_str(cls, use_secure_connection: bool = True) -> str:
+        return "mock"
+
     def __init__(self):
         super().__init__(endpoint_host='', endpoint_port=8888)