Add tests

[eheydrick]

We should add tests for these plugins. This will help catch issues that arise when Elasticsearch makes breaking changes. It will also ensure quality when we make changes, such as a change to the elasticsearch gem version. The tests should be executed against all versions of ES that we support, which is currently 1.x, 2.x, and 5.x.

[majormoses]

I would say that ES has EOL 1.x so we should drop support on it and we should focus on 2.x and 5.x: #48 (comment)

[majormoses]

oops accidental close...