Provide a full integration test for pkg_zip

pkg_zip should have an intergration test that
- builts a zip file using an instance of every supported feature
- unzips that file and inspects the file system for the expected results

Doing this with maximum fidelity requires, at a minimum, using the unzip tool which would be the logical default on any given OS. If there are multiple competitors, we would need to test against several versions. So, a robust integration test would require an "unzip" toolchain that finds the right unzip tool for each OS.

OTOH, doing this completely is a lot of work for little payoff. We currently have tests that use python zipfile to inspect .zip files to see if their content is as expected. The python code base has more testing resources thrown at it than we ever will. I expect it has closer fidelity to the expected behavior on any OS than we could ever achieve. I'm happy to go with the presumption that if the python zipfile module tells us we will get a file with specific attributes, so will the OS local 'unzip'.