Make 'gradle-home-cache-cleanup' more transparent

[bigdaz]

We've been getting some odd bug reports that seem to be related to gradle-home-cache-cleanup, but it's not exactly clear how.
We should add a little more logging so we know what cache cleanup is doing.

Ideas:

• Print contents of Gradle User Home before and after cache cleanup
• Run 'gradle' with --info or more when running cache cleanup build
• Print version of Gradle that runs cache cleanup