Bump up Consul version to 1.6.
Change persistent consul demo; instead of a separate namespace,
use a different label. This way, the two manifests can be more
similar; and this simplifies the demo flow.
In a few places, we were using 'Persistent Volume' the
wrong way. This was fixed.
Also added a whole chapter showing how to use local
persistent volumes, with an actually persistent
Consul cluster.