public ConfigChangeActions configChangeActions() {
        if (configChangeActions != null) return configChangeActions;
        throw new IllegalArgumentException("No config change actions: " + (prepared ? "was already prepared" : "not yet prepared"));
    }
@return config change actions that need to be performed as result of prepare
@throws IllegalArgumentException if called without being prepared by this
configserver/src/main/java/com/yahoo/vespa/config/server/deploy/Deployment.java