Java unit tests not running in CIs.

[mashhurs]

Description

We have rake test (eventually calls ./gradlew test) in Rakefile can be called in CI docker scripts. However, in CI execution (logstash-run.sh) it wasn't impossible to run since ./gradlew test rebuilds (has dependency on vendor task) the plugin and plugin requires LS source, env vars...
In a short term, they can be run in docker-setup.sh (Dockerfile -> RUN bundle exec rake vendor -> rake vendor to include task :vendor => [:install_jars, :test]) but it is a setup stage and we need to make sure setup stage should fail if Java tests fail.