Added type for bulk requests for Elastic search versions less than 7

[ShyamKunda]

Issue we are getting with Elastic search listener 2.6.5 and Elastic Search versions less than 7 .
ERROR i.g.d.j.b.e.ElasticSearchMetricSender: Exceptionorg.elasticsearch.client.ResponseException: method [POST], host [http://abc-analytics-elastic.xyx.net:9200], URI [/jmeter/_bulk], status line [HTTP/1.1 400 Bad Request] {"error":{"root_cause":[{"type":"action_request_validation_exception","reason":"Validation Failed: 1: type is missing;"}],"type":"action_request_validation_exception","reason":"Validation Failed: 1: type is missing;"},"status":400} 2019-07-04 11:20:55,244 ERROR i.g.d.j.b.e.ElasticSearchMetricSender: ElasticSearch Backend Listener was unable to perform request to the ElasticSearch engine. Check your JMeter console for more info. 2019-07-04 11:20:55,245 INFO o.a.j.g.u.JMeterMenuBar: setRunning(false, *local*)

[anthonygauthier]

@ShyamKunda : To avoid creating overhead, I changed where you were getting the version of the ElasticSearch instance (from the sendRequest() method to the setupTest() method). Would it be possible for you to still test if everything is okay with this?

If it is, I'll merge both the changes and release a new version.
Thanks,

[ShyamKunda]

@ShyamKunda : To avoid creating overhead, I changed where you were getting the version of the ElasticSearch instance (from the sendRequest() method to the setupTest() method). Would it be possible for you to still test if everything is okay with this?

If it is, I'll merge both the changes and release a new version.
Thanks,

Tested with Elastic search version 6.7.0 and 7.2.0. It is working fine.