Alert: NodeCPUUsage should be triggered when system's usage is high, not user's usage

[squirrelsc]

It's similar with #2760 , but this is for CPU.

Currently, the NodeCPUUsage alert will be triggered when node's CPU usage is higher than 98%. The bar is adjusted many times, and extremely high now. But there are still chance triggered by user's usage. So, there should be a way to check only system usage.

So the alert should be triggered when the system uses CPU than expected. But not triggered, when user uses 100% of requested CPU .

If user needs all CPU as requested, admin doesn't need care about it.

If system's processes uses more CPU than designed, there should be an alert. Even the free CPU is enough. As there may be a potential issue on system.