[2380] logged before updating an existing zone.

it can take time without any feedback while deleting old zone data,
so it's probably better to note that explicitly.

src/bin/loadzone/loadzone.py.in

@@ -245,6 +245,9 @@ class LoadZoneRunner:
             if created:
                 logger.info(LOADZONE_ZONE_CREATED, self._zone_name,
                             self._zone_class)
+            else:
+                logger.info(LOADZONE_ZONE_UPDATING, self._zone_name,
+                            self._zone_class)
             loader = ZoneLoader(datasrc_client, self._zone_name,
                                 self._zone_file)
             self.__start_time = time.time()

src/bin/loadzone/loadzone_messages.mes

@@ -70,3 +70,12 @@ in the data source.
 The SQLite3 data source is specified as the data source type without a
 data source configuration.  b10-loadzone uses the default
 configuration with the default DB file for the BIND 10 system.
+
+% LOADZONE_ZONE_UPDATING Started updating zone %1/%2 with removing old data (this can take a while)
+b10-loadzone started loading a new version of the zone as specified,
+beginning with removing the current contents of the zone (in a
+transaction, so the removal won't take effect until and unless the entire
+load is completed successfully).  If the old version of the zone is large,
+this can take time, such as a few minutes or more, without any visible
+feedback.  This is not a problem as long as the b10-loadzone process
+is working at a moderate load.