The syntax added in #39786 is great for being able to set up a custom multi-node demo cluster with different localities. However, it takes quite a bit of effort to learn and remember the syntax.

The goal of cockroach demo is to be dead simple, yet provide a realistic look at how CockroachDB works without having to set anything up ahead of time.

To this end, we should add default localities that are populated when you start a multi-node demo cluster. Let's make the default localities so that the cluster can be a reasonable shape no matter what you set the nodes argument to. I'm thinking:

region=us-east1,az=b
region=us-east1,az=c
region=us-east1,az=d
region=us-west1,az=a
region=us-west1,az=b
region=us-west1,az=c
region=europe-west1,az=b
region=europe-west1,az=c
region=europe-west1,az=d

This way, a 3-node cluster lives in us-east1, a 6-node cluster lives in us-east and us-west, and a 9-node cluster lives in us-east, us-west, europe-west.

@jseldess does this make sense to you as a reasonable default that might work for many types of demos?