libct/init: call Init from containerInit

Instead of having newContainerInit return an interface, and let its
caller call Init(), it is easier to call Init directly.

Do that, and rename newContainerInit to containerInit.

I think it makes the code more readable and straightforward.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/init_linux.go

@@ -167,52 +167,45 @@ func StartInitialization() (err error) {
 		}
 	}()
 
-	i, err := newContainerInit(it, pipe, consoleSocket, fifofd, logPipeFd, mountFds)
-	if err != nil {
-		return err
-	}
-
-	// If Init succeeds, syscall.Exec will not return, hence none of the defers will be called.
-	return i.Init()
-}
-
-type initer interface {
-	Init() error
+	// If init succeeds, it will not return, hence none of the defers will be called.
+	return containerInit(it, pipe, consoleSocket, fifofd, logPipeFd, mountFds)
 }
 
-func newContainerInit(t initType, pipe *os.File, consoleSocket *os.File, fifoFd, logFd int, mountFds []int) (initer, error) {
+func containerInit(t initType, pipe *os.File, consoleSocket *os.File, fifoFd, logFd int, mountFds []int) error {
 	var config *initConfig
 	if err := json.NewDecoder(pipe).Decode(&config); err != nil {
-		return nil, err
+		return err
 	}
 	if err := populateProcessEnvironment(config.Env); err != nil {
-		return nil, err
+		return err
 	}
 	switch t {
 	case initSetns:
 		// mountFds must be nil in this case. We don't mount while doing runc exec.
 		if mountFds != nil {
-			return nil, errors.New("mountFds must be nil; can't mount from exec")
+			return errors.New("mountFds must be nil; can't mount from exec")
 		}
 
-		return &linuxSetnsInit{
+		i := &linuxSetnsInit{
 			pipe:          pipe,
 			consoleSocket: consoleSocket,
 			config:        config,
 			logFd:         logFd,
-		}, nil
+		}
+		return i.Init()
 	case initStandard:
-		return &linuxStandardInit{
+		i := &linuxStandardInit{
 			pipe:          pipe,
 			consoleSocket: consoleSocket,
 			parentPid:     unix.Getppid(),
 			config:        config,
 			fifoFd:        fifoFd,
 			logFd:         logFd,
 			mountFds:      mountFds,
-		}, nil
+		}
+		return i.Init()
 	}
-	return nil, fmt.Errorf("unknown init type %q", t)
+	return fmt.Errorf("unknown init type %q", t)
 }
 
 // populateProcessEnvironment loads the provided environment variables into the