redis-trib.rb with auth

[aki.ta...@gmail.com]

We're using redis cluster(v4.0.1) with "requirepass" setting created by using redis-trib.rb.

Before using redis-trib.rb, we modified it referring to this page. 

https://github.com/antirez/redis/issues/3389

It seems like no problem now, but if you know the risk of modifying redis-trib.rb, please tell me about it.