Improve 2 tests do delete temporary files

Improve 2 tests do delete temporary files

There were some problems in file handling: One file in was not deleted
in case an exception was thrown during the test. Another case was a
JarFile which was not closed before deletion, which might work on Linux,
but not on Windows where the open file is still locked after usage.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>