Testing: Remove some left over files/dirs.

Testing: Remove some left over files/dirs.

When using tempfile.* in testing, those files get created
in the system tempdir. The docs say, we should try to
remove them.
Yes, the next reboot will clean them up also.

And in the workbench case, check after each test, that the
global workbench dir is empty (so the sub-workbcnhes have
been destroyed).