Schema validation failed: Data path "" should NOT have additional properties

### Bug Report or Feature Request (mark with an `x`)
```
- [x] bug report -> please search issues before submitting
- [ ] feature request
```

### Area
```
- [ ] devkit
- [x] schematics
```

### Versions
```
Angular CLI: 6.0.8
Node: 8.11.2
OS: win32 x64
Angular: 6.0.7
... animations, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, router

Package Version
-----------------------------------------------------------
@angular-devkit/architect 0.6.8
@angular-devkit/build-angular 0.6.8
@angular-devkit/build-optimizer 0.6.8
@angular-devkit/core 0.6.8
@angular-devkit/schematics 0.6.8
@angular/cli 6.0.8
@ngtools/webpack 6.0.8
@schematics/angular 0.6.8
@schematics/update 0.6.8
rxjs 6.2.1
typescript 2.7.2
webpack 4.8.3
```

### Repro steps

1. Add `projects/architect//options/invalid` options to `options` in `angular.json` eg
```
"build": {
"builder": "@angular-devkit/build-angular:browser",
"options": {
"invalid": "value",
...
}
}
```
2. Run `ng build`

### Actual functionality

```
Schema validation failed with the following errors:
Data path "" should NOT have additional properties(invalid).
```

### Desired functionality

```
Schema validation failed with the following errors:
Data path "path/to/invalid/option" should NOT have additional properties(invalid).
```

Commencez par suivre la validation du schéma pendant `ng build` pour les options de build de `angular.json` présentées dans la reproduction. Confirmez où l’option invalide est signalée et mettez à jour le diagnostic afin qu’il inclue le chemin de l’option concernée, puis vérifiez que la sortie correspond à la fonctionnalité attendue.

Rédigé par le modèle d'indexation à partir du texte de l'issue.