[close #383] fix integration test case flow_control & stop_downstream

[pingyu]

What problem does this PR solve?

Issue Number: close #383, close #393

Problem Description: integration test case flow_control/stop_downstream is flaky

What is changed and how does it work?

• Reuse allocated buffer for mq encoder.
• Fix incorrect calculation of encoder size.
• Reduce sarama.MaxRequestSize to reasonable value (1GiB -> 100MiB).
• Decrease record size of go-ycsb workload from 1KB to 250B.
• Retry PD connection with unlimited count.
• Fix flaky unit tests of mq_test & kafka_test.
• Add Grafana panel for Kafka sink.

Code changes

Check List for Tests

This PR has been tested by at least one of the following methods:

• Integration test

Side effects

• No side effects

Related changes

• No related changes

To reviewers

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[pingyu]

/test ?

[ti-chi-bot]

@pingyu: The following commands are available to trigger required jobs:

• /test pull-integration-kafka-test
• /test pull-integration-test
• /test pull-unit-test

Use /test all to run all jobs.

In response to this:

/test ?

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[pingyu]

/test pull-integration-kafka-test

[pingyu]

/test pull-integration-kafka-test

[pingyu]

/test pull-integration-kafka-test

[pingyu]

/test pull-integration-test

[pingyu]

/test pull-integration-kafka-test

[pingyu]

/test pull-integration-test

[pingyu]

/test pull-integration-test

[pingyu]

/test pull-integration-kafka-test

[pingyu]

/test pull-integration-kafka-test

[pingyu]

/test pull-integration-kafka-test

[pingyu]

/test pull-integration-test

[pingyu]

/test pull-integration-kafka-test

[pingyu]

/test pull-unit-test

[pingyu]

/test pull-unit-test

[pingyu]

/test pull-unit-test

[pingyu]

/test pull-unit-test