We assign the newly created nodes to multiple racks. If RF <= 3,
we create as many racks as the provided RF. We disallow the case
of RF > 3 to avoid trying to create an RF-rack-invalid keyspace;
note that no existing test calls `create_table_insert_data_for_repair`
providing a higher RF. The rationale for doing this is we want to ensure
that the tests calling the function can be run with the
`rf_rack_valid_keyspaces` configuration option enabled.
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