If we try to perform queries too early, before the call to
`storage_service::start_maintenance_mode` has finished, we will
fail with the following error:
```
ERROR 2025-11-12 20:32:27,064 [shard 0:sl:d] token_metadata - sorted_tokens is empty in first_token_index!
```
To avoid that, we should wait until initialization is complete.
Although setting the value of `maintenance_mode` to the string `"false"`
disables maintenance mode, the testing framework misinterprets the value
and thinks that it's actually enabled. As a result, it might try to
connect to Scylla via the maintenance socket, which we don't want.
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
