Instead of requiring the user to run the test suite with and without the
--use-old-replica-state flag, we introduce an 'old_replica_state()'
parametrized fixture that is used only when needed (i.e. in
test_cluster_{has_replica,node_count}.py).
* Change all replica status from `running` to `streaming`
* Add an option to pytest to change the state back to `running`
* Also tests the output of the script
* Add a quick test script for live clusters
