Use httphelper and cache response even when it is empty

Fixes https://github.com/owncloud/core/issues/12164
https://github.com/zendframework/ZendXml/pull/6

![500x375px-ll-b43ddc98_op_will_surely_deliver_weird_video_game_facts_part_7-s500x375-138152-535_zps9a4b13c9](https://cloud.githubusercontent.com/assets/195053/5199614/43547d4a-755e-11e4-8926-0d03fd29b1df.jpeg)