Update Setting's Robolectric tests' instructions

## The full suite

```

$ croot

$ make RunSettingsRoboTests

$ atest SettingsRoboTests

```

## Running a single test class

With a filter

```

$ croot

$ make RunSettingsRoboTests ROBOTEST_FILTER=<ClassName>

$ atest SettingsRoboTests:com.android.settings.display.AdaptiveSleepPreferenceControllerTest

```

For example:

You can also run any single test class with atest (it will try to find the correct path)

```

make RunSettingsRoboTests ROBOTEST_FILTER=CodeInspectionTest

$ atest AdaptiveSleepPreferenceControllerTest

```

You can also use partial class name in ROBOTEST_FILTER. If the partial class name matches

multiple file names, all of them will be executed.