ElasticSearch query runner: add support for skipping SSL certificate verification

[MrPortra]

Issue Summary

I tried to add a elasticsearch data source,Then I get error ：

connection refused.

I used curl --insecure -u admin:admin https://xxxx:9200/_cluster/health?pretty it seems well

I think it may have been caused by the use of SSL self signed certificate. How can I set skip TLS verification when I setup c data source?

Steps to Reproduce

1. setup data source
2. choose elasticsearch
3. write configuration
   4.test connection

Technical details:

• Redash Version: 4.0.1
• Browser/OS: N/A
• How did you install Redash: script

[arikfr]

Currently there is no such option (skip SSL verification).

If you want to implement this, we welcome pull requests :)