Merge branch 'stable-2.15' into stable-2.16

* stable-2.15:
  Add support for Elasticsearch version 7.4.*

Change-Id: Ic9bc8e16fc40e03e115c4a649fc3b4026ce1069a
tree: 1519883d8718a951c4cc6e24a9ee941a04020de0
  1. java/
  2. javatests/