Add golint to test (#255)

* Add a new lint rule to the Makefile

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

* Fix linter errors

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

* Allow replacing the default apt mirror

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

ctr/main.go

@@ -15,7 +15,7 @@ import (
 
 const usage = `High performance container daemon cli`
 
-type Exit struct {
+type exit struct {
 	Code int
 }
 
@@ -23,7 +23,7 @@ func main() {
 	// We want our defer functions to be run when calling fatal()
 	defer func() {
 		if e := recover(); e != nil {
-			if ex, ok := e.(Exit); ok == true {
+			if ex, ok := e.(exit); ok == true {
 				os.Exit(ex.Code)
 			}
 			panic(e)
@@ -86,5 +86,5 @@ var versionCommand = cli.Command{
 
 func fatal(err string, code int) {
 	fmt.Fprintf(os.Stderr, "[ctr] %s\n", err)
-	panic(Exit{code})
+	panic(exit{code})
 }