Configuration to control system service instances is potentially confusing

Description

The configuration in cdap-site.xml to control the number of instances of a system service is not used, except during the initial startup of CDAP.
It is checked and used only when the stored value is null or 0:
https://github.com/caskdata/cdap/blob/v4.1.1/cdap-master/src/main/java/co/cask/cdap/data/runtime/main/MasterServiceMain.java#L1024

A user might think they can shut down CDAP master, modify the value in cdap-site.xml, and start CDAP, and the configuration should take effect.
We should document that those values are only used in the very first execution of cdap master.

Also, YarnCheck is using the values in cdap-site.xml, whereas actual runtime will ignore them and use what's stored in ServiceStore.

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Bhooshan Mogal November 1, 2018 at 12:24 AM

please triage

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Created June 5, 2017 at 8:28 PM
Updated August 3, 2020 at 7:25 PM