Some minor cleanup of the sonar integration test.

+review REVIEW-5170
Simplify repository usage declaration.

+review REVIEW-5170
Closure -> Action, and tidy up of docs.

+review REVIEW-5170
Can't treat Properties as @InputFiles.

I'm not entirely sure @Input is right here either.

+review REVIEW-5170
Lazily create fork options to avoid doing unnecessary work when the task is not used.

+review REVIEW-5170
minor Javadoc improvements.

+review REVIEW-5170
method should be private.

+review REVIEW-5170
minor formatting.

+review REVIEW-5170
Need to make this package private for testing.

+review REVIEW-5170
Improved docs on sonar runner process.

+review REVIEW-5170
Don't need to compile against Sonar Runner anymore.

+review REVIEW-5170
Work on docs, and conversion of (most) public types to Java so that they are Javadoc'd instead of Groovydoc'd.

+review REVIEW-5170
Release notes for Sonar Runner improvements.

+review REVIEW-5170