Make load test and flame graph (when --perf enabled) running in parallel (#1011)
Make load test and flame graph (when --perf enabled) running in parallel (#1011)

* Make load test and flame graph (when enabled) running parallelly

* cleanup and fix python lint

* add process.join

* fix lint error
istio/tools,istio/tools,istio/tools,istio/tools,istio/tools,istio/tools