Browser opens long before webpack is ready

Right now, running `ionic serve` will use the Angular CLI's dev server, which uses webpack-dev-server. As far as I know, there isn't a way (via child processes) to know when the bundles are ready, aside from maybe parsing stdout of the process. This results in the Ionic CLI opening the browser window much sooner than expected and displaying a white screen until webpack-dev-server finally compiles everything and loads the app.

This message is displayed when the window is opened:

```
[ng] ℹ ｢wdm｣: wait until bundle finished: /
```

The Angular CLI used to have the same behavior if `--open` is specified, but it seems like it was fixed as of version 6.