Add indicators to stress benchmark

[kenny-y]

The current stress benchmark case (e.g. client-stress) is more like a round trip benchmark, it measures the round trip starting from a request being sent to the response being received. A stress benchmark of client-service is usually designed to measure (1) how many clients that a service can serve in parallel (2) how much resource it would consume (3) how much degradation of service quality when the number of clients grows... (there are others but let's just work the above 3 out)