Provide instrumentation configuration

[dodie]

Now the instrumentation happens automatically for every test class.
It would be more flexible if the user could specify the test classes or methods to be instrumented - for example with package whitelists or manually placed annotations in the test code.

I think keeping the Listener and the ability to add the Rule manually while providing an opt-out mechanism from the automatic instrumentation would provide flexibility for the users, in case of somebody prefers to manually select test classes for augmentation.

[dodie]

By default, Scott instruments methods with org.junit.Test annotations, and injects the ScottRule to every class that have at least one method with the org.junit.Test annotation.

This behaviour can be overridden with scott.track.method_annotation and the scott.injectrule.method_annotation JVM arguments.