[BEAM-4420] Add KafkaIO Integration Tests

[lgajowy]

This pr adds basic IOIT that can be run for 1000 records (there's only hashcode for 1000 records currently). To make the code review easier and because I'm not a Kafka expert, I took a baby steps approach here - after this PR is approved consequent PRs will provide:

• metrics collection
• hashes for bigger loads
• jenkins job to run automatically and on-demand & dashboards for them

I ran this test on existing kubernetes kafka cluster that is there in .test-infra folder (with success).

@aromanenko-dev @iemejia could you take a look?

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Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---		---	---
Java
Python		---			---	---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website
Non-portable
Portable	---		---	---

See .test-infra/jenkins/README for trigger phrase, status and link of all Jenkins jobs.

[iemejia]

Checkstyle not happy, you should use the vendored version of guava. Can you please also squash the commits into one with the proper title. Thanks.

[aromanenko-dev]

Thanks! Additionally to what Ismael said, I added several review comments

[lgajowy]

@iemejia @aromanenko-dev thanks for the review. I provided fixes.

@iemejia I didn't squash the commits on purpose - those are two atomic, independent changes. Having them as separate commits shows better why exactly something changed with proper commit titles and descriptions (see the description for the Kubernetes change). Squash will obfuscate this and will result with multiple unrelated changes in one commit. Other than that it will be easier to revert parts if needed. Suppose I was to revert only the Kubernetes change. Should I be forced to revert the whole test too?

[aromanenko-dev]

LGTM
Agree to keep two independent commits

[lgajowy]

Thanks!