Add clean tasks field to node

It is useful to differentiating nodes with unique clean tasks and corresponding parameters, For instance, admin can chose only run some clean steps for one node without restart conductor, or run a clean task with different parameters.
So create a new dict field clean_tasks in node to save clean tasks and it's parameters rather than save them in driver_internal_info. So that user should able to control this from API and this is can be done per node.