Schematics for Component spec should use test host component when created with `-cd OnPush`

### Versions
```
Angular CLI: 1.7.3
Node: 8.9.1
OS: win32 x64
Angular: 5.2.1
... animations, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, platform-server, router

@angular/cli: 1.7.3
@angular-devkit/build-optimizer: 0.3.2
@angular-devkit/core: 0.3.2
@angular-devkit/schematics: 0.3.2
@ngtools/json-schema: 1.2.0
@ngtools/webpack: 1.10.2
@schematics/angular: 0.3.2
@schematics/package-update: 0.3.2
typescript: 2.4.2
webpack: 3.11.0
```

### Repro steps
* `ng generate component test -cd OnPush`
* Edit the test.component.html to be
```
{{ checkMe() }}
```
* Add the checkMe method to test.component.ts:
```TypeScript
checkMe() {
console.log('change detection was invoked!');
}
```
* Edit the generated .spec file to include the following test:
```TypeScript
fit('runs change detection', () => {
fixture.detectChanges();
fixture.detectChanges();
fixture.detectChanges();
});
```
* Run unit test

### Observed behavior

'change detection was invoked!' is logged only once (the initial check on creation of the component) rather than 4 times. That is to say, invoking `fixture.detectChanges()` does not actually run change detection. This is a known issue and is discussed in https://github.com/angular/angular/issues/12313
```
LOG: 'change detection was invoked!'
Chrome 65.0.3325 (Windows 10 0.0.0): Executed 1 of 478 SUCCESS (0 secs / 0.138 secs)
```

### Desired behavior

As discussed in the thread linked above, the solution for testing OnPush components is to use the "test host component" pattern as described in the [angular.io testing docs](https://angular.io/guide/testing#component-inside-a-test-host).

Therefore, the Angular CLI should use a schematic which uses the test host component when the `-cd OnPush` flag has been used. Otherwise we get a default test setup which is not fit for purpose (and will cause many wasted hours for devs like me 😓)

Esegui `ng generate component test -cd OnPush` e ispeziona i file del componente generati e il file `.spec`, concentrandoti su come l'Angular component schematic configura i test. Usa come contesto le indicazioni collegate sui test di Angular, quindi verifica che il test generato utilizzi il pattern del componente host di test e che le chiamate ripetute a `fixture.detectChanges()` invochino il rilevamento delle modifiche.

Scritto dal modello di indicizzazione a partire dal testo della issue.