@Override
    public Reader getHosts() {
        try {
            File hostsFile = getHostsFile();
            if (!hostsFile.exists()) return null;
            return new FileReader(hostsFile);
        } catch (Exception e) {
            throw new IllegalArgumentException(e);
        }
    }
New package from given path on local file system. Retrieves config definition files from
the default location '$VESPA_HOME/share/vespa/configdefinitions'.

@param appDir application package directory
@param preprocessedDir preprocessed application package output directory
@param metaData metadata for this application package
@param includeSourceFiles include files from source dirs
config-application-package/src/main/java/com/yahoo/config/model/application/provider/FilesApplicationPackage.java