public void add(ClusterSpec cluster, Capacity capacity) {
        clusters.put(cluster.id(), cluster);
        capacities.put(cluster.id(), capacity);
    }
A recording of the capacity requests issued during a model build.
Requests are only recorded here if provision requests are issued to the node repo.

@author bratseth
config-model-api/src/main/java/com/yahoo/config/model/api/Provisioned.java