Returns a flag with the state of the SSH connection.

def is_alive(self):
        """Returns a flag with the state of the SSH connection."""
        null = chr(0)
        try:
            if self.device is None:
                return {"is_alive": False}
            else:
                # Try sending ASCII null byte to maintain the connection alive
                self._send_command(null)
        except (socket.error, EOFError):
            # If unable to send, we can tell for sure that the connection is unusable,
            # hence return False.
            return {"is_alive": False}
        return {"is_alive": self.device.remote_conn.transport.is_active()}