Enhance test for chown+hardlinks #1694

This test is a bit weird, it only works because both the file and the hardlink are under the same monitored directory, which means this is effectively the same as test_chown. We can leave it for now, but we might want to add some tests (in a follow-up PR) that run on the host using root access, look at the tests in test_mount.py to see how you can mark the tests to be skipped in non-root users.

Originally posted by @Molter73 in #1468 (comment)