fix new cluster tests issues (#9657)

Following #9483 the daily CI exposed a few problems.

* The cluster creation code (uses redis-cli) is complicated to test with TLS enabled.
  for now i'm just skipping them since the tests we run there don't really need that kind of coverage
* cluster port binding failures
  note that `find_available_port` already looks for a free cluster port
  but the code in `wait_server_started` couldn't detect the failure of binding
  (the text it greps for wasn't found in the log)