Ensure we log into logrus on command error

`urfave/cli` now takes upon itself to log the error returned by the
command action directly. This means that by default the `--log` option
was ignored upon error.

This commit ensure that `urfave/cli.ErrWriter` will use logrus

Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"strings"
 
@@ -45,6 +46,8 @@ your host. Providing the bundle directory using "-b" is optional. The default
 value for "bundle" is the current directory.`
 )
 
+var originalCliErrWriter io.Writer
+
 func main() {
 	app := cli.NewApp()
 	app.Name = "runc"
@@ -129,7 +132,22 @@ func main() {
 		}
 		return nil
 	}
+	// If the command returns an error, cli takes upon itself to print
+	// the error on cli.ErrWriter and exit.
+	// Use our own writer here to ensure the log gets sent to the right location.
+	originalCliErrWriter = cli.ErrWriter
+	cli.ErrWriter = &FatalWriter{}
 	if err := app.Run(os.Args); err != nil {
 		fatal(err)
 	}
 }
+
+type FatalWriter struct {
+}
+
+func (FatalWriter) Write(p []byte) (n int, err error) {
+	msg := string(p)
+	logrus.Error(msg)
+	fmt.Fprint(originalCliErrWriter, msg)
+	return len(p), nil
+}