test/tools/javac/diags/Example.java leaves directories in tempdir

When the test runs it creates temporary directories in java.io.tmpdir in the
case of unix it is /var/tmp, unfortunately the test does not clean up
after itself. Thus on a shared system there is a possibility of permission
issue and perhaps even clobbering/unpredictable results, if multiple
regression tests are running at the same time by the same user.

One should use the current directory, this is a unique scratch directory
created by jteg for this very purpose of creating transient files and
will be cleaned up on exit.