Change data used for topic readiness check

[rodion-goritskov]

Problem: I am trying to use Openmessaging Benchmark for the performance testing of our in-house message broker. However, we have strict message schema validation, so probing the producers doesn't work for us, as it only sends an empty byte array.

Solution: Send the same messages used for testing.

[rodion-goritskov]

@teabot @merlimat

[teabot]

This sounds like a good idea.

[rodion-goritskov]

@merlimat Got log4j updated - tests should pass now

[stale[bot]]

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