[Documentation] Contributing guide is not updated or confusing

[imdhemy]

Summary of problem or feature request

I followed the contributing guide. When I tried to run the RestSpecRunner I got the following error:

ERROR: Host https://localhost:9200 is offline

After some research I found that the RestSpecRunner is not using the environment variable ES_TEST_HOST, but
instead it is using the ELASTICSEARCH_URL here.

When I set the ELASTICSEARCH_URL, the RestSpecRunner works fine and the unit tests are passing.

I did the same with integration tests, all of them are passing except the MlTest which requires a platinum license if I'm not mistaken.

Questions

• Should the documentation be updated to refer to ELASTICSEARCH_URL?
• Should all integration tests pass on local machines? If yes, Is there any guide for that?

[ezimuel]

@imdhemy thanks for opening this issue. I'll fix the documentation asap.