ElasticContainer: Use Elasticsearch 6.4.2 for V6_4 tests

This is a cherry-pick of stable-2.15 recently merged commit 3797753.
This pick assumes that Elasticsearch 6.x.y is still also maintained for
the stable-2.14 branch.

Version 6.4.2 is the latest release on the 6.4.x series.

Change-Id: I615aa08b1bf5d924022ef421cb9ed35e7154068c
1 file changed
tree: 606d9bb30e0d3c27c4d11605db5ee0826db8fdbd
  1. gerrit-acceptance-tests/
  2. gerrit-elasticsearch/
  3. gerrit-pgm/