Fixes JERSEY-2515 - after checking that it is possible to create files i...

...n java.io.tmpdir by attempting to create a file there, it should be deleted immediately
You're fast :) I don't want to be PITA but would it be possible for you to change `java.io.tmpdir` to original value in the afterClass method? I can do it as an internal commit if you have no time for it.