'Shuffle the list. The current client swaps position with its successor.
If maintain_index is True the current_index is adjusted,
such that the same client stays current and goes down in list.'

def shuffle_down(self, maintain_index=True):

    idx = self._current_idx
    if ((idx + 1) < len(self.clients)):
        (self.clients[idx], self.clients[(idx + 1)]) = (self[(idx + 1)], self[idx])
        if maintain_index:
            self.current_index += 1
