fix when rpc reports "transport is closing" error, health check go routine will exit

Signed-off-by: Wentao Zhang <zhangwentao234@huawei.com>

libcontainerd/remote_unix.go

@@ -154,7 +154,7 @@ func (r *remote) handleConnectionChange() {
 		logrus.Debugf("libcontainerd: containerd health check returned error: %v", err)
 
 		if r.daemonPid != -1 {
-			if strings.Contains(err.Error(), "is closing") {
+			if r.closeManually {
 				// Well, we asked for it to stop, just return
 				return
 			}