Auth failed occasionally

[jetz]

Hi @leporo

I set redis requirepass xxxxx, and use tornado-redis like:

self.conn = tornadoredis.Client(host='127.0.0.1',
                                port=6379,
                                password='xxxxx',
                                selected_db=15)

Most of the time, it's ok, but occasionally, auth failed when use blpop（timeout=30）,following is traceback:

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/tornado/web.py", line 1348, in _execute
    result = yield result
  File "/usr/local/lib/python2.7/site-packages/tornado/gen.py", line 807, in run
    value = future.result()
  File "/usr/local/lib/python2.7/site-packages/tornado/concurrent.py", line 209, in result
    raise_exc_info(self._exc_info)
  File "/usr/local/lib/python2.7/site-packages/tornado/gen.py", line 810, in run
    yielded = self.gen.throw(*sys.exc_info())
  File "server.py", line 269, in get
    step = yield self.broker.get_step(sid, timeout=30)
  File "/usr/local/lib/python2.7/site-packages/tornado/gen.py", line 807, in run
    value = future.result()
  File "/usr/local/lib/python2.7/site-packages/tornado/concurrent.py", line 209, in result
    raise_exc_info(self._exc_info)
  File "/usr/local/lib/python2.7/site-packages/tornado/stack_context.py", line 314, in wrapped
    ret = fn(*args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/tornado/gen.py", line 131, in final_callback
    if future.result() is not None:
  File "/usr/local/lib/python2.7/site-packages/tornado/concurrent.py", line 209, in result
    raise_exc_info(self._exc_info)
  File "/usr/local/lib/python2.7/site-packages/tornado/gen.py", line 812, in run
    yielded = self.gen.send(value)
  File "/usr/local/lib/python2.7/site-packages/tornadoredis/client.py", line 444, in execute_command
    result = self.format_reply(cmd_line, resp)
  File "/usr/local/lib/python2.7/site-packages/tornadoredis/client.py", line 383, in format_reply
    % (cmd_line, data, e), cmd_line
ResponseError: ResponseError (on BLPOP [('step:tewptefHdXxbCi1kkUUwGTfH', 30), {}]): failed to format reply to BLPOP(('step:tewptefHdXxbCi1kkUUwGTfH', 30),{}), raw data: ResponseError (on BLPOP [('step:tewptefHdXxbCi1kkUUwGTfH', 30), {}]): NOAUTH Authentication required.; err message: sequence index must be integer, not 'slice'

NOAUTH Authentication required, then raise ResponseError, which can't be formated by format_reply.