feat: support rendezvous after spawn done

Change-Id: I4b07a88b61da4dc1863b189db9eb831ffb14130a

internal/boomer/boomer.go

@@ -127,3 +127,11 @@ func (b *Boomer) RecordFailure(requestType, name string, responseTime int64, exc
 func (b *Boomer) Quit() {
 	b.localRunner.stop()
 }
+
+func (b *Boomer) IsSpawnDone() bool {
+	return b.localRunner.isSpawnDone
+}
+
+func (b *Boomer) GetSpawnCount() int {
+	return b.localRunner.spawnCount
+}

internal/boomer/runner.go

@@ -63,6 +63,7 @@ type runner struct {
 	spawnCount        int   // target clients to spawn
 	spawnRate         float64
 	loop              *Loop // specify running cycles
+	isSpawnDone       bool
 
 	outputs []Output
 }
@@ -193,6 +194,7 @@ func (r *localRunner) spawnWorkers(spawnCount int, spawnRate float64, quit chan
 		}
 	}
 
+	r.isSpawnDone = true
 	if spawnCompleteFunc != nil {
 		spawnCompleteFunc()
 	}