[2013] add log for config update failure

src/bin/ddns/ddns.py.in

@@ -216,6 +216,7 @@ class DDNSServer:
             # complicated and it's not clear how much validation is performed
             # there, so, while assuming it's unlikely to happen, we act
             # proactively.
+            logger.error(DDNS_CONFIG_HANDLER_ERROR, ex)
             return create_answer(1, "Failed to handle new configuration: " +
                                  str(ex))
 

src/bin/ddns/ddns_messages.mes

@@ -104,3 +104,11 @@ process will now shut down.
 The b10-ddns process encountered an uncaught exception and will now shut
 down. This is indicative of a programming error and should not happen under
 normal circumstances. The exception type and message are printed.
+
+% DDNS_CONFIG_HANDLER_ERROR failed to update ddns configuration: %1
+An update to b10-ddns configuration was delivered but an error was
+found while applying them.  None of the delivered updates were applied
+to the running b10-ddns system, and the server will keep running with
+the existing configuration.  If this happened in the initial
+configuration setup, the server will be running with the default
+configurations.