This gets us ready to add writing to Redis from ocsp-updater. The Go
redis client requires different configuration for cluster operation
than non-cluster, so we need to simulate a cluster in our integration
environment. Cluster operation requires a manual initialization step,
which you can do like so:
```
docker-compose up -d bredis docker-compose exec bredis bash
/test/redis-create.sh
```
I still need to figure out how to make that happen automatically during
integration tests and when you run docker-compose up.
The hex values in redis.config are randomly generated passwords for the
different users.
Fixes#5723
Jacob Hoffman-Andrews