waitForLogger doesn't work as intended with the Elasticsearch back-end

[23Skidoo]

Code fragment that illustrates the issue: abdd45f#diff-5ae59c4cdd155945a87b6ce91090551fR27

At least on my machine, I had to add calls to threadDelay after calls to logging functions to ensure that messages actually get written, even though I call waitForLogger before proceeding. Not sure yet whether the problem is on our or the Elasticsearch side.

[23Skidoo]

This looks like a feature of Elasticsearch: data becomes visible only after ~1 second. The way to fix this is to make waitForLogger use Elasticsearch refresh API: https://www.elastic.co/guide/en/elasticsearch/guide/current/near-real-time.html#refresh-api