Revert OperatingSystemMXBean to previous impl and update the logic

[chamilaadhi]

Purpose

reverting #75 and update OperatingSystemMXBean to work with jdk 11 with minimal code change

This pr change OperatingSystemMXBean to the previous state and only add the following section as a change (add the condition clause). From JDK9 onwards these method were made public. so explicitly calling the setAccessible cause issues in jdk11

    if (!Modifier.isPublic(method.getModifiers())) {
        method.setAccessible(true);
    }