private Optional<Reader> optionalFile(Path filePath) {
        try {
            return Optional.of(getFile(filePath).createReader());
        } catch (FileNotFoundException e) {
            return Optional.empty();
        }
    }
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