Pull Request: https://github.com/edx/edx-platform/pull/7258
Description: DjangoKeyValueStore.set_many was causing multiple writes whenever it saved data for a newly created XBlock. It called FieldDataCache.find_or_create which, if the block wasn't cached, did a get_or_create call to create it. Then DjangoKeyValueStore immediately called save on that block. This results in both an insert of empty state, and then an update of that record.