Install redis to run at startup

With the latest changes to vagrant, provisioning is only run on the first `vagrant up`. This means that your provisioning scripts should set any services up to run at boot.

This updates `init.sh` to do that, and also make sure that the latest stable version of redis is installed, using the recommended settings and steps from the [Redis QuickStart](http://redis.io/topics/quickstart)

This also has the benefit of upgrading redis to the latest stable version with a simple `vagrant provision`.