Merge branch 'stable-2.14' into stable-2.15

* stable-2.14:
  ElasticReindexIT: Add tests against Elasticsearch version 6
  Elasticsearch: Add tests for queries against version 6
  Elasticsearch: Add support for V6 / one index type

The changes done in I04f275dd9 ("ElasticReindexIT: Add tests against
Elasticsearch version 6") are not included in this merge since the
reindex tests currently don't work on stable-2.15 (see issue 8799).

Change-Id: I1c940f6a95d39710dc7fb8c1cac605fa4c8efac6
tree: ddc833ddd54bcd85e8883563b2ceffd4f2b28165
  1. gerrit-acceptance-tests/
  2. gerrit-elasticsearch/
  3. gerrit-pgm/