rkt: Wrap exec errors as utilexec.ExitError

This is needed by the exec prober to distinguish error types and exit
codes correctly.

An alternative, and preferable solution would be to use utilexec
everywhere, but that change is much more involved and should come at a
later date. Unfortunately, until that change is made, writing tests for
this is quite difficult.

pkg/kubelet/rkt/rkt.go

@@ -1857,6 +1857,13 @@ func (r *rktExitError) ExitStatus() int {
 	return 0
 }
 
+func newRktExitError(e error) error {
+	if exitErr, ok := e.(*exec.ExitError); ok {
+		return &rktExitError{exitErr}
+	}
+	return e
+}
+
 func (r *Runtime) AttachContainer(containerID kubecontainer.ContainerID, stdin io.Reader, stdout, stderr io.WriteCloser, tty bool) error {
 	return fmt.Errorf("unimplemented")
 }
@@ -1891,7 +1898,7 @@ func (r *Runtime) ExecInContainer(containerID kubecontainer.ContainerID, cmd []s
 		if stdout != nil {
 			go io.Copy(stdout, p)
 		}
-		return command.Wait()
+		return newRktExitError(command.Wait())
 	}
 	if stdin != nil {
 		// Use an os.Pipe here as it returns true *os.File objects.
@@ -1900,7 +1907,7 @@ func (r *Runtime) ExecInContainer(containerID kubecontainer.ContainerID, cmd []s
 		// of the pipe.
 		r, w, err := r.os.Pipe()
 		if err != nil {
-			return err
+			return newRktExitError(err)
 		}
 		go io.Copy(w, stdin)
 
@@ -1912,7 +1919,7 @@ func (r *Runtime) ExecInContainer(containerID kubecontainer.ContainerID, cmd []s
 	if stderr != nil {
 		command.Stderr = stderr
 	}
-	return command.Run()
+	return newRktExitError(command.Run())
 }
 
 // PortForward executes socat in the pod's network namespace and copies