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).
Instead of defining the CliRunner value in each test, we use a fixture.
The CliRunner is also configured with stdout and stderr separated
because mixing them will pose problem if we use stderr for other
purposes in tests, e.g. to emit log messages from a forth-coming HTTP
server.
* 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
