### Preflight Checklist
* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details
```js
let ret = shell.openItem('file:///noexistent');
console.log(ret);
```
`ret` is always `true` on Linux even if opening fails, e.g.
```sh
xdg-open 'file:///noexistent'
echo $?
```
Shows nonzero error code.

* **Electron Version:**
  * v6.0.11
* **Operating System:**
  *Linux / Ubuntu 16.04 x64

### Expected Behavior
`ret` should be `false`, if `xdg-open` returns non-zero code.

Optional: It would be very nice if the `xdg-open` error (catch stderr) would be displayed in `dialog.showErrorBox` if it returns non-zero code. Just take care that `xdg-open` may write some warnings to stderr even if it returns 0.

shell/common/api/atom_api_shell.cc
gin_helper::Arguments* args) {
  base::win::ShortcutOperation operation = base::win::SHORTCUT_CREATE_ALWAYS;
  args->GetNext(&operation);
  gin::Dictionary options = gin::Dictionary::CreateEmpty(args->isolate());
  if (!args->GetNext(&options)) {
    args->ThrowError();
    return false;
  }
  base::win::ShortcutProperties properties;
  base::FilePath path;
  base::string16 str;
  int index;
  if (options.Get("target", &path))
    properties.set_target(path);
  if (options.Get("cwd", &path))
    properties.set_working_dir(path);
  if (options.Get("args", &str))
    properties.set_arguments(str);
  if (options.Get("description", &str))
    properties.set_description(str);
  if (options.Get("icon", &path) && options.Get("iconIndex", &index))
    properties.set_icon(path, index);
  if (options.Get("appUserModelId", &str))
    properties.set_app_id(str);
  base::win::ScopedCOMInitializer com_initializer;
  return base::win::CreateOrUpdateShortcutLink(shortcut_path, properties,
                                               operation);
}
v8::Local<v8::Value> ReadShortcutLink(gin_helper::ErrorThrower thrower,