Add integration tests for ElasticsearchIO

In https://github.com/apache/incubator-beam/pull/1439#pullrequestreview, the original PR included a dockerfile and an integration test that ran against an ES instance in that dockerfile.

We are working on infrastructure to stand up docker containers for this kind of testing, but aren't quite ready for it, so we pulled the scripts, dockerfile+IT out of that PR. This issue tracks checking that work in once we can take advantage of it.