chown-recursive: let's rework the recursive logic to use O_PATH

That way we can pin a specific inode and analyze it and manipulate it
without it being swapped out beneath our hands.

Fixes a vulnerability originally found by Jann Horn from Google.

CVE-2018-15687
LP: #1796692
https://bugzilla.redhat.com/show_bug.cgi?id=1639076