Failed sentinel connection doesn't report Error

[SamBergeron]

Hi, if I start a new connection with an array of sentinels where none are valid, no error is reported in the error listener. This is not the same behavior as with a single server connection.

Here is what I see with an invalid redis connection (or a down server) with debug enabled:

  ioredis:redis status[192.168.56.1:6379]: connecting -> close +1ms
  ioredis:connection reconnect in 400ms +0ms
  ioredis:redis status[192.168.56.1:6379]: close -> reconnecting +0ms
  ioredis:redis status[192.168.56.1:6379]: reconnecting -> connecting +400ms
  ioredis:connection error: Error: connect ECONNREFUSED 192.168.56.1:6379 +2ms
2017-03-31T15:49:03.012Z - error: Redis client error: Error: connect ECONNREFUSED 192.168.56.1:6379

The last log message being the one printed by redis.on('error', ...

Here is what I see when I have invalid (or down) sentinels

  ioredis:redis status[192.168.56.1:26379]: [empty] -> connecting +219ms
  ioredis:redis queue command[0] -> sentinel(get-master-addr-by-name,nteredis) +0ms
  ioredis:connection error: Error: connect ECONNREFUSED 192.168.56.1:26379 +2ms
  ioredis:redis status[192.168.56.1:26379]: connecting -> close +0ms
  ioredis:redis status[192.168.56.1:26379]: close -> end +0ms
  ioredis:SentinelConnector failed to connect to sentinel 192.168.56.1:26379 because Error: Connection is closed. +1ms
  ioredis:redis status[192.168.56.1:26378]: [empty] -> connecting +0ms
  ioredis:redis queue command[0] -> sentinel(get-master-addr-by-name,nteredis) +0ms
  ioredis:connection error: Error: connect ECONNREFUSED 192.168.56.1:26378 +2ms
  ioredis:redis status[192.168.56.1:26378]: connecting -> close +0ms
  ioredis:redis status[192.168.56.1:26378]: close -> end +0ms
  ioredis:SentinelConnector failed to connect to sentinel 192.168.56.1:26378 because Error: Connection is closed. +0ms
  ioredis:SentinelConnector All sentinels are unreachable. Retrying from scratch after 230 +0ms
  ioredis:redis status[localhost:6379]: end -> end +1ms

As you can see there is no log message caught in redis.on('error', ....
The mechanism work fine, if I turn the sentinels back on they will reconnect, but there is no way of knowing what is happening if DEBUG=ioredis* isn't turned on.

[SamBergeron]

Possible fix with #446