test.py suite.yaml prepare_cql doesn't support non-idempotent statements

[avikivity]

prepare_cql is executed on every test, instead on every cluster.

[kostja]

How would you like to see it fixed? Another suite_yaml option which runs once per cluster?

[nyh]

In #18771 I got rid of the "prepare_cql" thing in the Alternator test suite. Is it used anywhere else? Maybe we can drop it?

In any case, I agree that if we keep it, the idea was (I think...) to run it once after the cluster is created (to "prepare" the cluster for all the tests), and not once before every test.