Merge branch '2681-elasticsearch-retry' into 'master'

Elasticsearch queries should retry on failure

Closes #2681

See merge request !2181

changelogs/unreleased-ee/2681-elasticsearch-retry.yml

+---
+title: Retry Elasticsearch queries on failure
+merge_request: 2181
+author:

lib/gitlab/elastic/client.rb

@@ -10,7 +10,7 @@ module Gitlab
       # Takes a hash as returned by `ApplicationSetting#elasticsearch_config`,
       # and configures itself based on those parameters
       def self.build(config)
-        base_config = { urls: config[:url] }
+        base_config = { urls: config[:url], retry_on_failure: true }
 
         if config[:aws]
           creds = resolve_aws_credentials(config)