Upgrade elasticsearch-rest-client to 6.4.0

In this version several variants of the RestClient's performRequest
method are deprecated [1].

Adjust the implementation to use the recommended variant instead.

[1] https://www.elastic.co/guide/en/elasticsearch/reference/6.x/breaking_64_rest_client_changes.html

Change-Id: Ib09ab0a0800ed6957060c6e04352605ac5424062
3 files changed
tree: 4a7e2b7bd092fd8195b8d53cce95902406f3cbd2
  1. gerrit-acceptance-tests/
  2. gerrit-elasticsearch/
  3. gerrit-pgm/