Working AndroidTestOrchestrator example

AndroidTestOrchestrator example would be nice. The JavaDoc instructions are not working for me.

```
*

Whereas previously you might have called {@code am instrument -w
* com.example.app/android.support.test.runner.AndroidJUnitRunner} you would now execute {@code
* 'CLASSPATH=$(pm path com.google.android.apps.common.testing.services) app_process /
* android.support.test.services.shellexecutor.ShellMain am instrument -w -e targetInstrumentation
* com.example.app/android.support.test.runner.AndroidJUnitRunner
* android.support.test.orchestrator/android.support.test.orchestrator.AndroidTestOrchestrator'}
```

I always get an error. The links to download the relevant apks are also missing.

Comienza revisando el comando de AndroidTestOrchestrator JavaDoc y los ejemplos existentes de testing-samples. Reproduce el error de instrumentación informado, añade un ejemplo funcional y enlaces a los APK relevantes, y verifica que el comando documentado funcione.

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