Implement logging strategy (#444)

* Logging strategy and convert all prints() to logging invocations

trustgraph-flow/trustgraph/query/triples/cassandra/service.py

@@ -4,11 +4,16 @@ Triples query service.  Input is a (s, p, o) triple, some values may be
 null.  Output is a list of triples.
 """
 
+import logging
+
 from .... direct.cassandra import TrustGraph
 from .... schema import TriplesQueryRequest, TriplesQueryResponse, Error
 from .... schema import Value, Triple
 from .... base import TriplesQueryService
 
+# Module logger
+logger = logging.getLogger(__name__)
+
 default_ident = "triples-query"
 
 default_graph_host='localhost'
@@ -135,7 +140,7 @@ class Processor(TriplesQueryService):
 
         except Exception as e:
 
-            print(f"Exception: {e}")
+            logger.error(f"Exception querying triples: {e}", exc_info=True)
             raise e
 
     @staticmethod