Add Dockerfile (and some small changes to fix build)

[roiravhon]

@jayme-github, thanks for that! Looks good.

Tested it?

[jayme-github]

Yes, it's tested and I've set up auto-build here: https://hub.docker.com/r/traumfewo/elasticsearch-stress-test/

Run it like:

docker run --rm -it --link elasticsearch:es-test traumfewo/elasticsearch-stress-test:latest \
    --es_address es-test --indices 10 --documents 10 \
    --clients 1 --seconds 300

# or something like
kubectl run -it --rm es-stress --image=traumfewo/elasticsearch-stress-test:latest --restart Never -- \
    --es_address es-test --indices 10 --documents 10 --clients 1 --seconds 300

[roiravhon]

Thanks!