Add helper for useTestNG setting options on test

[JLLeitschuh]

Something like this should be sufficient:

fun Test.useTestNG(options: TestNGOptions.() -> Unit) {
    useTestNG(closureOf(options))
}

Not sure where this should be added.

[eskatos]

Thanks for the report @JLLeitschuh

It applies to a bunch of Test task's methods, e.g. useJUnit is affected too.
We need to add type-safe methods for these in the Test task to fix this properly.

[eskatos]

See gradle/gradle#1202