Support Elasticsearch v6 in Elasticsearch preset

[orlangure]

Until now I only tried to run Elasticsearch v7 in all tests, and elasticsearch client v7 is used for health checks and initialization. To allow testing earlier versions of elasticsearch, we should seamlessly support v6 images, and make needed adjustments transparently.

There is a chance that the code will work with elasticsearch v as-is. Or maybe we will only need to use a different package version (the client has v6 and v7 packages). There is also a chance that some setup functions or a health check implementation won't work on v6.

In the end, a user should be able to use v6 and v7 versions (WithVersion) and still get a working and ready-to-use container in the end.