Report expected and last returned rcode on query timeout

Sometimes it's useful to see what was the server returning that did not
match the expected rcode.

bin/tests/system/isctest/query.py

@@ -48,6 +48,11 @@ def generic_query(
         except (dns.exception.Timeout, ConnectionRefusedError) as e:
             isctest.log.debug(f"{query_func.__name__}(): the '{e}' exceptio raised")
         time.sleep(1)
+    if expected_rcode is not None:
+        last_rcode = dns_rcode.to_text(res.rcode()) if res else None
+        isctest.log.debug(
+            f"{query_func.__name__}(): expected rcode={dns_rcode.to_text(expected_rcode)}, last rcode={last_rcode}"
+        )
     raise dns.exception.Timeout