ElasticRestClientProvider: Detect Elasticsearch version

On initialization of the client, make a GET request to the Elasticsearch
server and parse the version out of the response.

Log the version at info level.

In follow-up commits, the version will be stored and used to change the
structure of queries based on which Elasticsearch version is used.

Change-Id: I693b54d008b24191c66dbf16815a223441d22d43
2 files changed
tree: fceffcdb1debe0e5a488a0d3fc4d41aaab5d04a8
  1. gerrit-acceptance-tests/
  2. gerrit-elasticsearch/
  3. gerrit-pgm/