private String readConfigDefinition(File defPath) {
        try (Reader reader = retrieveConfigDefReader(defPath)) {
            return IOUtils.readAll(reader);
        } catch (IOException e) {
            throw new RuntimeException("Error reading config definition '" + defPath + "'", e);
        }
    }
Creates a reader for a config definition

@param defPath the path to the application package
@return the reader of this config definition
config-application-package/src/main/java/com/yahoo/config/model/application/provider/FilesApplicationPackage.java