Utilize linearization results for validate watch

[serathius]

What would you like to be added?

Implement following TODO

etcd/tests/robustness/validate/validate.go

Lines 43 to 44 in e4d1da7

	// TODO: Use requests from linearization for replay.
	replay := model.NewReplay(persistedRequests)

Thanks to anishathalye/porcupine#21 (comment) we should be able to extract linearization results and use them to validate watch.

Why is this needed?

Restores blackbox testing property of validating watch. Instead of needing to look under the hood of etcd WAL history we can just use the requests send by client.