UP-4177 richer unit test and idiomatic Groovy looping

Refactor and richer unit test for `AttributeDuplicatingPersonAttributesScript` that was introduced in #408 .

 * Use idiomatic forEach in groovy ( `for (desiredName in desiredNames) {` )
 * use `assertEquals` rather than Java `assert` keyword in unit test
 * test the full content of the resulting attribute map against expected beyond just testing the resulting size.