Remove choosePort and rely on dynamic, OS-allocated ports during tests

[ewencp]

No description provided.

[ewencp]

Works in conjunction with confluentinc/rest-utils#90 and avoids Address already in use errors during tests due to choosePort not being a reliable way to select a random available port. Will probably need some work/follow up PRs to make it merge up through all recent branches, especially due to recent addition of Kafka-based coordination.

[rayokota]

@ewencp , this looks reasonable. Are we still interesting in getting this in?

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