Disabling native2ascii has no effect within the Gradle build (Version 3.2.7 and above)

Disabling `native2ascii` in `application.yml` has no effect with the WAR creation process. According to the [documentation](http://docs.grails.org/latest/guide/conf.html#builtInOptions) this configuration should disable the `native2ascii` task.

### Steps to Reproduce

1. Use Grails 3.2.7 (or higher) and run `grails create-app native2ascii`
2. Change directory `cd native2ascii`
2. Modify `application.yml`

```
grails:
enable:
native2ascii: false
```

3. Run `grails clean && grails war`
4. Take a look at `cat build/resources/main/messages_de.properties` and expect no UTF-8 escaped stuff such as `\u00f6`

### Expected Behaviour

The properties file should get copied **without** escaping non ASCII characters to UTF-8 codes.

### Actual Behaviour

The properties file should get copied with escaping non ASCII characters to UTF-8 codes.

### Environment Information

- **Operating System**: macOS

| Grails Version: 3.2.7
| Groovy Version: 2.4.10
| JVM Version: 1.8.0_121

Start with application.yml and reproduce the issue using `grails clean && grails war` in a Grails 3.2.7+ application created by `grails create-app native2ascii`. Inspect build/resources/main/messages_de.properties and the WAR build path; done means disabling native2ascii prevents non-ASCII characters from being escaped.

Written by the indexing model from the issue text.