private boolean isUsedOn(AllocatedHosts hosts, Version version) {
        return hosts.getHosts().stream()
                               .anyMatch(host -> host.version().isPresent() && host.version().get().equals(version));
    }
Returns the subset of the given versions which are in use on these hosts
configserver/src/main/java/com/yahoo/vespa/config/server/modelfactory/ModelsBuilder.java