Description of problem:
In OSP8 we introduced authentication for the Redis service so we need to add the following to the docs:

1. Passing Redis password as a parameter during the deployment. Build an environment file or add the following parameter to an existing environment:

parameter_defaults:
  RedisPassword: 'examplepassword'

By default the password is generated by the tripleoclient so you cannot know it to build the loadbalancer configuration before the deployment.

2. An example HAProxy configuration for Redis:
listen redis
  bind 172.16.20.249:6379 
  balance first
  option tcp-check
  tcp-check connect
  tcp-check send AUTH\ examplepassword\r\n
  tcp-check send PING\r\n
  tcp-check expect string +PONG
  tcp-check send info\ replication\r\n
  tcp-check expect string role:master
  tcp-check send QUIT\r\n
  tcp-check expect string +OK
  server overcloud-controller-0 172.16.20.150:6379 check fall 5 inter 2000 rise 2
  server overcloud-controller-1 172.16.20.151:6379 check fall 5 inter 2000 rise 2
  server overcloud-controller-2 172.16.20.152:6379 check fall 5 inter 2000 rise 2


Note the ' tcp-check send AUTH\ examplepassword\r\n' line where the password needs to match the RedisPassword parameter.