|T151324 [epic] System level upgrade for cirrus / elasticsearch
|T154501 [Epic, Q3 Goal] Upgrade search systems to Elasticsearch 5
|T155506 Replace custom reindexing code with the Elasticsearch 5 reindex api
Patch works for the common use case, i need to spend some more time testing it locally. Even once merged we will probably want to try it on some larger indexes on relforge or some such to make sure what it does on small indices with a thousand documents is also sane on multi-million document indices.