Merge branch 'stable-2.15' into stable-2.16

* stable-2.15:
  Set version to 2.15.8-SNAPSHOT
  ElasticTestUtils: Factor common code out of ElasticReindexIT/ElasticIndexIT
  Add support for Elasticsearch 6.5.0
  Add Marco Miller as a developer in pom.xml files
  Set version to 2.14.17

Change-Id: I0bb655abd6a158f09f670ad65cd37f70479fe483
tree: f58bd9307844f80f926d8a0504dbe5f5b4ea9502
  1. java/
  2. javatests/