Elasticsearch: Support and use v6.6.0 for testing

Bump the elasticsearch-rest-client version to 6.6.0, accordingly.

None of the breaking changes mentioned in [1] negatively impact this
integration, according to console output of the 'elastic' tagged tests.

[1] https://www.elastic.co/guide/en/elasticsearch/reference/current/release-notes-6.6.0.html

Change-Id: I4908254ebda9a2a8296b1fe7b174065637485a03
8 files changed
tree: 45bb258f3ddc8211dfd43db27db32670745b852b
  1. gerrit-acceptance-tests/
  2. gerrit-elasticsearch/
  3. gerrit-pgm/