We adapt the existing code to work across all zones in a region.

We require a feature-flag to enable Ubernetes-Lite

Reasons:

* There are some behavioural changes if users create volumes with
the same name in two zones.
* We don't want to make one API call per zone if we're not running
Ubernetes-Lite.
* Ubernetes-Lite is still experimental.

There isn't a parallel flag implemented for AWS, because at the moment
there would be no behaviour changes from this.