private List<HostSpec> prepare(NodeRepositoryProvisioner provisioner) {
            return clusterContexts.stream()
                    .map(clusterContext -> clusterContext.prepare(provisioner))
                    .flatMap(List::stream)
                    .toList();
        }
Returns list of cluster specs of this application.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/testutils/MockDeployer.java