Add propagate=0 for loggers in logging.conf-sample

Otherwise messages from zuul and gerrit loggers are printed
twice: from the logger and from root logger.

Change-Id: I377758d4b70e250f8b2ba281cd0dabcf12555b62

etc/logging.conf-sample

@@ -15,11 +15,13 @@ handlers=console
 level=DEBUG
 handlers=debug,normal
 qualname=zuul
+propagate=0
 
 [logger_gerrit]
 level=DEBUG
 handlers=debug,normal
 qualname=gerrit
+propagate=0
 
 [handler_console]
 level=WARNING