Merge branch 'stable-2.15' into stable-2.16

* stable-2.15:
  Bazel: Enable Error-Prone by default
  Parallelize account migration in schema 146 migration
  Fix _nextStepHandle not being assigned a value when scrolling
  Elasticsearch: Remove redundant handling of 'ignore_unmapped' property
  Elasticsearch: Fix support for V6 versions earlier than 6.7.*
  ElasticVersionTest: Add missing assertions on V6_7

Change-Id: Ib655c541a28e3a9a2197465a58e1eff12123c6a5
tree: 492c21a4ae3979b2392476074a57f9073492af38
  1. java/
  2. javatests/