PerfTestMulti: "elapsed" timestamp issue in 2.19.0.RC2

[eibbojtir]

When running PerfTestMulti from 2.18, the elapsed timestamps increment as expected in the resulting JSON file. In 2.19.0.RC2 the timestamps don't increment as expected. See sample below where the elapsed time of 70954835876 does not increment:

{
  "max-pro-2": {
    "send-bytes-rate": 0.0,
    "recv-msg-rate": 12474.984375,
    "avg-latency": 15653412,
    "send-msg-rate": 11874.958984375,
    "recv-bytes-rate": 0.0,
    "samples": [
      {
        "elapsed": 70954835876,
        "send-bytes-rate": 0.0,
        "recv-msg-rate": 0.0,
        "send-msg-rate": 137400.390625,
        "recv-bytes-rate": 0.0
      },
      {
        "elapsed": 70954835876,
        "send-bytes-rate": 0.0,
        "recv-msg-rate": 9.2E9,
        "max-latency": 936463,
        "min-latency": 11516,
        "avg-latency": 234714,
        "send-msg-rate": 5.3525999616E10,
        "recv-bytes-rate": 0.0
      },
      {
        "elapsed": 70954835876,
        "send-bytes-rate": 0.0,
        "recv-msg-rate": 6.14793472E9,
        "max-latency": 1714879,
        "min-latency": 1026688,
        "avg-latency": 1371234,
        "send-msg-rate": 4.0359268352E10,
        "recv-bytes-rate": 0.0
      },
{
        "elapsed": 70954835876,
        "send-bytes-rate": 0.0,
        "recv-msg-rate": 2.095099904E10,
        "max-latency": 2908040,
        "min-latency": 2074701,
        "avg-latency": 2598572,
        "send-msg-rate": 5.3528997888E10,
        "recv-bytes-rate": 0.0
      },
      {
        "elapsed": 70954835876,
        "send-bytes-rate": 0.0,
        "recv-msg-rate": 2.416E10,
        "max-latency": 3866366,
        "min-latency": 2446476,
        "avg-latency": 3361168,
        "send-msg-rate": 5.9938000896E10,
        "recv-bytes-rate": 0.0
      },
      {
        "elapsed": 70954835876,
        "send-bytes-rate": 0.0,
        "recv-msg-rate": 2.4161998848E10,
        "max-latency": 4743201,
        "min-latency": 2145754,
        "avg-latency": 3657347,
        "send-msg-rate": 5.7564000256E10,
        "recv-bytes-rate": 0.0
      },