Add support for Elasticsearch 6.4.0

According to the release notes [1] there are several breaking changes,
but none of them seem to affect Gerrit's integration.

Update the version manager and adapter to recognize 6.4.* as a supported
version, and modify the test container to use 6.4.0 for the V6 tests.

Update the reindex and ssh index tests to also test against 6.4.0.

[1] https://www.elastic.co/guide/en/elasticsearch/reference/current/release-notes-6.4.0.html

Bug: Issue 9670
Change-Id: If0d16df1a719d45aad9c56409e14c8fcf3945bd5
9 files changed
tree: f521978725b71f3d9bc9f352a6b12c24f56a6379
  1. gerrit-acceptance-tests/
  2. gerrit-elasticsearch/
  3. gerrit-pgm/