How to Clean old tasks shown with Started at = N/A and Duration = N/A in Red Hat Satellite 6

Issue

• On Satellite server old tasks shown with "Started at = N/A" an "Duration = N/A" are not getting cleaned.

  Action   State   Result  Started at  Duration    Operation
  ==================================================================
  Run Sync Plan:   scheduled   pending N/A   N/A
  InsightsCloud::Async::InsightsScheduledSync  scheduled   pending N/A   N/A
  ForemanInventoryUpload::Async::GenerateAllReportsJob scheduled   pending N/A   N/A
  Run Sync Plan: Core Products RH Workstation  stopped cancelled   N/A   N/A
  Run Sync Plan: Core Products stopped cancelled   N/A   N/A