Use different result directories when running not full test suite

I often want to run one part of test and then another. There are 2 problems: after running tests for same variant, but different run configuration (e.g. different class name or size), test results from first run are overwritten or tests not run at all. It apparently depends on whether Gradle decides tests need to be rerun.

With this patch Gradle will treat spoon runs with different configuration as effectively different tasks, and treat results accordingly.