It is mostly copy of the reload() method. Currently, it does not contain
the initialization of load_action for the zone writer, so if a real zone
writer is returned, it doesn't work (it throws). But the tests for the
unsuccessful cases succeed.

There's also need to do something about the duplicate code between this
method and the reload(). Later on, we'll probably rewrite reload to use
the ZoneWriter (and even later deprecate reload, maybe? Or keep it as
the thin wrapper for convenience?)