Improvements for logging on order.setback()

Current Situation

• The log message SCHEDULER-947 setback(): order has been set back... is created at warning level.
• This warning doesn't give any information why the order was setback and may cause confusion if no setback is configured.

Desired Behavior

• The log message SCHEDULER-947 setback(): order has been set back... is switched from warning level to info level.
  • It is better if the job implementation itself creates a warning if an order can no longer be set back.
  • The job implementation has to know if an order could not be set back anymore, e.g. because the max setback intervall has been reached.
• Therefore the method order.setback() needs to return a boolean value:
  • true - the order was set back and will be processed again later.
  • false - the order could not be set back any more.
• A reason can be specified why the taks finally failed if not further setback is performed.
  • The method spooler_task.set_reasion("...") as specified by JS-1310 can be used to store that information.

Proposed Usage

• A common usage example would be:

  if (!order.setback()) spooler_log.warn("Failed to find...");