Service management of Sage - D

[YU_Xinjie]

I suggest we add a "sage config VAR_NAME" command, so that app of Sage (such as GLAD) can query the config value easily.

It is needed for many situations:
1. We need to use "atp_cnt" to set up glad_size of GLAD.
2. GLAD needs the config.node info.

@lingu

Please endorse.