Add logging about subreaper

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

containerd/main.go

@@ -103,6 +103,9 @@ func daemon(id, stateDir string, concurrency, bufferSize int) error {
 	}
 	// only set containerd as the subreaper if it is not an init process
 	if pid := os.Getpid(); pid != 1 {
+		logrus.WithFields(logrus.Fields{
+			"pid": pid,
+		}).Debug("containerd is not init, set as subreaper")
 		if err := setSubReaper(); err != nil {
 			return err
 		}