Specify loggsaver in the runner to collect log from main container.

This commit specifies the container to collect the logs from when
there are more than one run contaienrs exit.

tools/runner/logsaver.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 
 	grpcv1 "github.com/grpc/test-infra/api/v1"
+	"github.com/grpc/test-infra/config"
 	"github.com/grpc/test-infra/status"
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -79,7 +80,7 @@ func (ls *LogSaver) getTestPods(ctx context.Context, loadTest *grpcv1.LoadTest)
 }
 
 func (ls *LogSaver) getPodLogBuffer(ctx context.Context, pod *corev1.Pod) (*bytes.Buffer, error) {
-	req := ls.podsGetter.Pods(pod.Namespace).GetLogs(pod.Name, &corev1.PodLogOptions{})
+	req := ls.podsGetter.Pods(pod.Namespace).GetLogs(pod.Name, &corev1.PodLogOptions{Container: config.RunContainerName})
 	driverLogs, err := req.Stream(ctx)
 	if err != nil {
 		return nil, err