Enforce comparison test

[dai-chen]

Last year we developed a test framework which verifies result by comparing with other SQL implementation. It was integrated with Gradle task to automate the testing. However, due to problems in old codebase, it was only used for reporting instead of being mandatory for plugin build. Now as we start shift to new query engine, the success of comparison test results should be enforced. Reference: https://github.com/opendistro-for-elasticsearch/sql/blob/develop/docs/dev/Testing.md.