[JENKINS-24399] A test to reproduce JENKINS-24399

This is a demonstration for [JENKINS-24399] (https://issues.jenkins-ci.org/browse/JENKINS-24399) Modifying files in class directories can bypass approval in script-security (or class directories are accepted as classpaths).
Do not merge.

script-security 1.5 allows to use a class directory as an additional classpath.
This test shows that users can use class directories whose contents are modified without administrators' approval.