Returns a boolean flag with the state of the connection.

def is_alive(self):
        """Returns a boolean flag with the state of the connection."""
        null = chr(0)
        if self.remote_conn is None:
            log.error("Connection is not initialised, is_alive returns False")
            return False
        if self.protocol == "telnet":
            try:
                # Try sending IAC + NOP (IAC is telnet way of sending command)
                # IAC = Interpret as Command; it comes before the NOP.
                log.debug("Sending IAC + NOP")
                # Need to send multiple times to test connection
                self.remote_conn.sock.sendall(telnetlib.IAC + telnetlib.NOP)
                self.remote_conn.sock.sendall(telnetlib.IAC + telnetlib.NOP)
                self.remote_conn.sock.sendall(telnetlib.IAC + telnetlib.NOP)
                return True
            except AttributeError:
                return False
        else:
            # SSH
            try:
                # Try sending ASCII null byte to maintain the connection alive
                log.debug("Sending the NULL byte")
                self.write_channel(null)
                return self.remote_conn.transport.is_active()
            except (socket.error, EOFError):
                log.error("Unable to send", exc_info=True)
                # If unable to send, we can tell for sure that the connection is unusable
                return False
        return False