private static Object getStaticField(final Class<?> clazz, final String fieldName) throws LogbackException {
        try {
            final Field field = clazz.getField(fieldName);
            return field.get(null);
        } catch (final ReflectiveOperationException ex) {
            throw new LogbackException(ex);
        }
    }
Configures Logback's root logger.

<p>It calls Logback's configurators through reflection so that embulk-core does not need to depend on Logback's classes.
embulk-core/src/main/java/org/embulk/cli/CliLogbackConfigurator.java