Merge the Isilon ATF code

This is a placeholder merge request to go over all of the items to ensure that I understand everything, some of the items from Isilon can be dropped as I dropped them from the atf branch (diff reduction), and make sure that any valid fixes from NetBSD can be pushed back.
Discussion being done in NetBSD PR bin/49005. I'm convinced that what we should do at this point though is create a dummy file in the Makefile, install it to the tests directory, then try and run the test as a unprivileged user (it's part of what I noted in the PR).