tests: in_dummy: try and wait for the first record before doing checks.

[pwhelan]

Summary

Add a busy wait loop for in_dummy checks that wait around 5 seconds or for the first record before tests check record count. This should make tests less flaky when running on hosted multi-tenant environments.

I ran the test several times while running sysbench, similar to my previous log test fix.

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Testing
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Backporting

• Backport to latest stable release.

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[edsiper]

commit needs to be "tests: runtime: in_symple_system:.." , fixed by squashing the PR