Ping the LDBD Server and return any message received back as a string.

    @return: message received (may be empty) from LDBD Server as a string

def ping(self):
    """
    Ping the LDBD Server and return any message received back as a string.

    @return: message received (may be empty) from LDBD Server as a string
    """

    msg = "PING\0"
    self.sfile.write(msg)

    ret, output = self.__response__()
    reply = str(output[0])

    if ret:
      msg = "Error pinging server %d:%s" % (ret, reply)
      raise LDBDClientException, msg

    return reply