Big change here is that we start to use ES's base test clases for
testing. This should give us access to randomized testing and makes
sure that the reproduction lines are correct.
Original commit: elastic/x-pack-elasticsearch@bcab64a028
Make the projects more like the rest of Elasticsearch:
* Move integration tests from `itest` to `test`
* Make a build file per sql subproject
* Make sql work properly with elasticsearch-extra
Original commit: elastic/x-pack-elasticsearch@6fbb794f68
