Allow routers to control when users are loaded

The binlogrouter requires that users are not loaded at startup. This
allows it to inject the service user into the list of valid MySQL users so
that the binlogrouter can be controlled via the listeners.

server/modules/routing/binlog/blr.c

@@ -1793,7 +1793,7 @@ static void rses_end_locked_router_action(ROUTER_SLAVE *rses)
 
 static int getCapabilities()
 {
-    return (int)RCAP_TYPE_NO_RSESSION;
+    return (int)(RCAP_TYPE_NO_RSESSION | RCAP_TYPE_NO_USERS_INIT);
 }
 
 /**