Add the ability to send/recv to/from the OS using polling, `WouldBlock` sys-calls about crossbeam HOT 2 OPEN

pub struct BootstrapTcpListener {
    poll: Poll,
    events: Events,
    server: TcpListener,
    // HACK : create variable to move ownership of mio_server to the thread
    // if mio_server is not moved, poll does not receive any event from listener
    _mio_server: MioTcpListener,
}

pub enum PollEvent {
    NewConnection((TcpStream, SocketAddr)),
    Stop,
}

impl BSEventPoller for BootstrapTcpListener {
    fn poll(&mut self) -> Result<PollEvent, BootstrapError> {
        self.poll.poll(&mut self.events, None).unwrap();

        // Confirm that we are not being signalled to shut down
        if self.events.iter().any(|ev| ev.token() == STOP_LISTENER) {
            return Ok(PollEvent::Stop);
        }

        // Ther could be more than one connection ready, but we want to re-check for the stop
        // signal after processing each connection.
        return Ok(PollEvent::NewConnection(
            self.server.accept().map_err(BootstrapError::from)?,
        ));
    }
}

impl BootstrapListenerStopHandle {
    /// Stop the bootstrap listener.
    pub fn stop(self) -> Result<(), BootstrapError> {
        self.0.wake().map_err(BootstrapError::from)
    }
}

loop {
    let conn = select! {
        recv(stopper_rx) -> _ => return Ok(()),
        recv(conn_rx) -> conn => conn,
    };
    // ...validate connection before dispatching to a system-thread to handle
}