util/io: add RedirectStderr

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

util/io/redirect.go

@@ -0,0 +1,17 @@
+package io
+
+import (
+	"os"
+	"sync"
+)
+
+var osStderrMu sync.Mutex
+
+var OrigStderr = func() *os.File {
+	fd, err := dupFD(os.Stderr.Fd())
+	if err != nil {
+		panic(err)
+	}
+
+	return os.NewFile(fd, os.Stderr.Name())
+}()