How to disable captive portal detection? How to remove exclamation mark on Wi-Fi or signal icon in lollipop?

When connected to the Internet, the system checks if it's in a walled garden, which is simply trying to connect to google. If it fails, in Android 5, there'll be an exclamation mark on the wifi icon or signal icon.

In some situations, this is annoying. Say, in China, google is blocked, the exclamation mark will always be there, which is meaningless.

How can I disable this check, and make the system assume, connected wifi/mobile data is connected Internet?

The solution to this question is the same as to this question: How can I stop Lollipop ignoring my wifi network? but I can't answer there, so I'll post a new question and answer it myself.