Index the content when the syncing finishes
Index only when synchronization not handled by Dynflow action

The Actions::Katello::Repository::Sync itself handled then indexing of
the content: no need to do it again the after_sync callback.
Fix indexing after scheduled tasks

Wrong class caused task.progress to return hash that doesn't have
error_details method.
Merge pull request #3785 from iNecas/index-content-after-sync

Index the content when the syncing finishes