[Improvement] Add indicators to judge whether the node is healthy

[smallzhongfeng]

At present, there is only disk i/o in the health detection of the machine. Whether to add the index of memory utilization? What do u think of that? @jerqi

[jerqi]

At present, there is only disk i/o in the health detection of the machine. Whether to add the index of memory utilization? What do u think of that? @jerqi

A heath check about memory utilization?