Merge branch 'stable-3.1'

* stable-3.1:
  e2e-tests: Add JAVA_OPTS support to the framework
  Documentation: Refactor how-to-contribute heading
  Documentation: Group community index links together
  ElasticV{6,7}QueryChangesTest: Add comment about issue 10120

Change-Id: Id4ead5634206b8542d2acf571e3aecd23d0eb228
tree: b80deddcb85045f7eb88a0891469246aafe1f2a5
  1. java/
  2. javatests/