Some cluster tests use `cluster_con` when they need a different load
balancing policy or auth provider. However, no test uses a port
other than 9042 or enables SSL, but all tests must pass `9042, False`
because these parameters don't have default values. This makes the code
more verbose. Also, it's quite obvious that 9042 stands for port, but
it's not obvious what `False` is related to, so there is a need to check
the definition of `cluster_con` while reading any test that uses it.
No reason to backport, it's only a minor refactoring.
Closesscylladb/scylladb#25516
