fail better when running --profile or --release against android emulators

Currently we fail w/:

```
flutter run --release
Cannot locate file: /Users/devoncarew/projects/flutter/flutter/bin/cache/artifacts/engine/android-x64-release/icudtl.dat
Failure building APK: unable to find components.
```

But we should emit a better message, like: `emulators only support --debug`.
