Upgrade elasticsearch-rest-client to 6.5.2
Upgrade elasticsearch-rest-client to 6.5.2

According to the release notes [1] there are no REST client related
changes. This is just to keep up-to-date with the latest version.

[1] https://www.elastic.co/guide/en/elasticsearch/reference/current/release-notes-6.5.2.html

Change-Id: I0569a12ec96078905bed4996209d826e43fe108b

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