WIP: Add Redis Dockerfiles

Creating Dockerfiles for `base_redis`, `redis_master` and `redis_slave`. 

# Base Redis

This will install a new-ish version of redis from `ppa:chris-lea/redis-server`. It is intended to be used as a base image for the master and slave dockerfiles.

# Redis Master

This is the standard redis image definition. It acts as a primary redis server and can be combined with 0 or more slaves for failover.

# Redis Slave

Zero or more of the slave instances can be added to create a redis cluster.

See the README files of each image for more details