libcontainer: handle error cases

Handle err return value of fmt.Scanf, os.Pipe and unix.ParseUnixRights.

Found with honnef.co/go/tools/cmd/staticcheck

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

libcontainer/integration/execin_test.go

@@ -431,7 +431,13 @@ func TestExecinPassExtraFiles(t *testing.T) {
 
 	var stdout bytes.Buffer
 	pipeout1, pipein1, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
 	pipeout2, pipein2, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
 	inprocess := &libcontainer.Process{
 		Cwd:        "/",
 		Args:       []string{"sh", "-c", "cd /proc/$$/fd; echo -n *; echo -n 1 >3; echo -n 2 >4"},