Merge branch 'huacnlee/current-settings-autoload-bug-in-development' into 'master'

Fix CurrentSettings autoload bug in development

_Originally opened at !2526 by @huacnlee._

- - -

In development env, when we changed any file hit Rails reload, it will failed with this message:

```
A copy of Gitlab::CurrentSettings has been removed from the module tree but is still active
```

See merge request !2753