MXS-936: add shutdown hooks

First part: add shutdown hooks for routers.

Binlog is the first one with a  destroyInstance() routine

server/modules/routing/cli/cli.c

@@ -71,7 +71,8 @@ static ROUTER_OBJECT MyObject =
     diagnostics,
     NULL,
     NULL,
-    getCapabilities
+    getCapabilities,
+    NULL
 };
 
 extern int execute_cmd(CLI_SESSION *cli);