The list of active print jobs in print service retunring wrong result.

1. The getActivePrintJobs() method in print service is designed to return
   the active print job i.e. ones scheduled to be processed by the print
   service. Now the correct list is returned.

2. The listeners for observing the state of print jobs may be called even
   after being unregistered. Ex: state change occurs and we schedule a
   message on the app's main thread to make the notificaion. Now the app
   unregisretes the callback and on the next loop the notification message
   is handled.

bug:11200258

Change-Id: I4a497b5c9a7287a22023cafe41ce966d14300ca6