[FLINK-25771][connectors][Cassandra][tests][flaky] Reduce cassandra testContainer load to avoid timeouts and in general flakiness issues

[echauchot]

I took a look at the history of flaky test and found that:
testCassandraBatchTupleFormat failure https://dev.azure.com/apache-flink/apache-flink/_build/results?buildId=32816&view=results
testCassandraScalaTuplePartialColumnUpdate failure https://dev.azure.com/apache-flink/apache-flink/_build/results?buildId=32571&view=resultstestCassandraScalaTuplePartialColumnUpdate
testCassandraTableSink failure https://dev.azure.com/apache-flink/apache-flink/_build/results?buildId=32272

They fail because the keyspace does not exist while executing create table (in before) whereas the keyspace is created in before class. My guess it that drop tables (in after) is not atomic and drops the keyspace in between. Hence my commit for making it atomic.

The other failures I see are timeouts in only testRetrialAndDropTables method. But this test is no more relevant as the table names are now dynamic. Simply remove this test

R: @XComp

[flinkbot]

CI report:

• 492a13f Azure: SUCCESS

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[echauchot]

@zentol, I analyzed the problem. OperationTimeoutException definitely happens at the client side (Cassandra driver) under load in all the tests but the timeouts raised seem to be not enough. So I reduced the load by avoiding "IF EXIST" in CQL requests and more important I replaced drop keyspace by drop table. Indeed, each Before updates the tableID and it is called even in case or retrials. So, we need to drop only the created table for this test (with the same tableID) and not the whole keyspace. That will reduce the overall load on cassandra (so I hope no more timeouts) but also fix the keyspace does not exist flaky issue.

Finally I put testRetrialDropTable back to check that everything still works in case of retrial (drop the single table instead of keyspace etc...)

I did 10 local runs of the whole CassandraITCase with no error.

[echauchot]

@zentol Actually, dropTable() is no more even needed because each test including retrials use a different table name now. I also removed the leftover flink_initial table. I don't know what it was for.
So we lower the load even more.
PTAL

[zentol]

you can just remove it, no need for a comment. I don't remember why we had this in the first place.

[echauchot]

yes, that is what I already did in the latest commits

[zentol]

no you didn't, its still there :)

[echauchot]

oops, my bad. Done

[echauchot]

@flinkbot run azure

[echauchot]

@zentol I addressed all your comments. It should be ok now. PTAL

[echauchot]

thanks @zentol for reviewing and merging !