kotlin-dsl-plugin-bundle.kt

Make build compatible with latest Gradle snapshot distro
- Remove usages of extensions referencing
`DomainObjectProvider` (now renamed `NamedDomainObjectProvider`)
- Make all references to `test` task lazy (eager references were
causing a ConcurrentModificationException on the TestKit classpath
computation)
- Let `pluginBundle.plugins` be created by `java-gradle-plugin` plugin