Make the "demo" generic

[gbartolini]

Currently the "demo" only creates two static clusters: pg-eu and pg-us. What about repeating what we have done in the main setup and the monitoring one to accept a list of clusters?

As a convention, we could do something like this:

./demo/setup.sh eu us

Which assumes a circular relationship eu->us->eu ... and so on for the distributed topology. Cluster names will be prepended by 'pg-'.

For a simple local setup with no distributed topology we could accept a name:

./demo/setup.sh local

You can accept even more than two regions:

./demo/setup.sh eu us au

Which assumes eu->us->au and back to eu.