Refactor code to use "all" instead of "all_ids"

lib/tasks/thumbnail.rake

@@ -13,7 +13,7 @@ namespace :thumbnail do
 
       begin
         # Get items from dspace (from offset to offset+limit)
-        items_ids = item_database_repository.all_ids(limit,offset)
+        items = item_database_repository.all(limit,offset)
       rescue
         # Sleeps for a while to wait database's recovery
         sleep(30.seconds)
@@ -21,13 +21,13 @@ namespace :thumbnail do
         next
       else
         # Terminate loop if there are no more items to import
-        break if items_ids.empty?
+        break if items.empty?
 
         # Increment offset, to get new items on next iteration
         offset = offset + limit
 
-        items_ids.each do |id|
-          ThumbnailGeneratorWorker.perform_async(id)
+        items.each do |item|
+          ThumbnailGeneratorWorker.perform_async(item.id)
         end
 
       end