Fix tests for Elasticsearch adapter

[flyaruu]

The elasticsearch adapter (we used it for cashless in Sendrato I think) has no meaningful tests. I'd like some tests to insert data into a local index and then assert that the data is actually there.

We can run an Elasticsearch container using circleci. As an example, you can take a look at the mongodb tests, in the Enterprise circleci config we start a mongodb instance for testing as well

We could also consider moving it to enterprise