static SharedHosts empty() {
        return new SharedHosts() {
            @Override public boolean supportsClusterType(ClusterSpec.Type clusterType) { return false; }
            @Override public boolean hasClusterType(ClusterSpec.Type clusterType) { return false; }
        };
    }
Whether there are any shared hosts specifically for the given cluster type.
config-provisioning/src/main/java/com/yahoo/config/provision/SharedHosts.java