File versionFile() {
        return versionFile;
    }
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