Listener::waitUntilListening may return before listening has started

The waitUntilListening function uses a condition wait with a predicate based on the bool Listener::_ready. Unfortunately, this variable is not initialized in the constructor, meaning that its value is indeterminate. In the case where it is indeterminately a numeric value interpretable as 'false', callers to waitUntilListening will return immediately, before listening has actually started.

Note that repl::isSelf depends on the proper functioning of waitUntilListening, since otherwise it may attempt to connect before the socket is listening, leading to a false negative.