benchmark: exit after printing help when using `-h` (#2701)
benchmark: exit after printing help when using `-h` (#2701)


menghanl/grpc-go,stanley-cheung/grpc-go,stanley-cheung/grpc-go,dfawley/grpc-go,grpc/grpc-go,dfawley/grpc-go,menghanl/grpc-go,grpc/grpc-go