Merge back evgeny-goldin/spock-extensions version of TempDirectory

The current spock-extensions fork from Evgeny Goldin, while good, has a few too many dependencies. I only wanted the @TempDirectory, and your repo is clearly the originator of this idea. I back ported some of this changes which specifically call the directory the name of the test and put it in the build/test directory by default. This works much better for us, since we don't want to clutter up the /tmp directory. I know that these are pretty opinionated, so feel free to just ignore this pull request, I'm just throwing it out there.

I also moved the deleting of the folder till after cleanup, since in essence we're wrapping the test, so just like we go before setup, we should go after cleanup. I talked to @pniederw and he agreed. He also hinted that this will be built into Spock directly someday.