public boolean isUpgraded() {
        Version storedVersion = storedVersion();
        if (storedVersion.equals(Version.emptyVersion)) return true;

        // TODO: Also verify version for downgrades?
        if (currentVersion().compareTo(storedVersion) > 0) {
            verifyVersionIntervalForUpgrade(storedVersion);
            return true;
        } else {
            return false;
        }
    }
Contains version information for this configserver. Stored both in file system and in ZooKeeper (uses
data in ZooKeeper if distributeApplicationPackage and data found in ZooKeeper)

@author Ulf Lilleengen
@author hmusum
configserver/src/main/java/com/yahoo/vespa/config/server/version/VersionState.java