[FLOC-1043] ELK Acceptance test

Fixes https://clusterhq.atlassian.net/browse/FLOC-1043

This has the flaw of not actually testing that the data shows up in Kibana. It does test the linking feature - between Elasticsearch and logstash, and Kibana needs to be set up (these test verifies that it is running). We could e.g. use selenium and check that there is no error saying that Kibana cannot find Elasticsearch, and trust that if it can find the data store then it will display it as in the tutorial. I'd like feedback on what is a sensible approach, and whether any work on that can be a separate issue.

This script avoids so many race conditions. Once this has been reviewed, I will try / make an issue for manually running the tutorial as fast as possible and see if there are places where that should be warned against.

When merging, each dependency must also go in the internal documentation for packages used.

edit, from another PR:  "Anyone reviewing this should note that Buildbot currently skips the acceptance tests because it looks for nodes running on the tutorial IP addresses and skips if they can't be reached. Unfortunately this means that tests should be run locally to check that they pass."
This idiom is unnecessary, `.addCallback` just returns the same Deferred again. So you can just return `sendin_messages`.