test: allow to start a replicaset without waiting

It is needed to verify the `supervised` bootstrap strategy. We should
start the instances, issue `box.ctl.make_bootstrap_leader` and only than
wait for `config:info().status == 'ready'`.

Let's support this flow in the replicaset management helper.

Part of #8862

NO_DOC=testing helper change
NO_CHANGELOG=see NO_DOC