investigate test failures with es 6

[jillesvangurp]

Currently the tests don't pass with Elasticsearch v6. As there were not a lot of changes between 6 and 7, it may be possible to get them to pass.

Run elasticsearch like so:

docker run -p 9999:9200 -p 9300:9300 -e "discovery.type=single-node" docker.elastic.co/elasticsearch/elasticsearch:6.8.23

Run the tests with

./gradlew :search-client:build

Multiple tests fail trying to create the test document index:

ElasticsearchStatusException[Elasticsearch exception [type=mapper_parsing_exception, reason=Failed to parse mapping [properties]: Root mapping definition has unsupported parameters:  [number : {type=double}] [tag : {type=keyword}] [message : {type=text}]]]; nested: ElasticsearchException[Elasticsearch exception [type=mapper_parsing_exception, reason=Root mapping definition has unsupported parameters:  [number : {type=double}] [tag : {type=keyword}] [message : {type=text}]]];

Not super critical, but would be nice to figure this out.

[jillesvangurp]

wontfix