private Set<RegionName> prodRegions(List<Step> steps) {
        return steps.stream()
                    .flatMap(s -> s.zones().stream())
                    .filter(zone -> zone.environment().isProduction())
                    .flatMap(z -> z.region().stream())
                    .collect(Collectors.toSet());
    }
A bcp instance as written and imported may either specify groups containing all regions,
or no groups, meaning it should contain one group with all regions.
This adds that missing implicit group when appropriate.
config-model-api/src/main/java/com/yahoo/config/application/api/xml/DeploymentSpecXmlReader.java