The current implementation of `rmtree` will try to fix permissions
when it encounters permission errors during its operation. This is
done by opening the target via `os.open` and then adjusting the
immutable flag and the permission bits. This is a problem when the
target is a broken symlink since open will fail with `ENOENT`. A
simple reproducer of this scenario is:
$ mkdir subdir
$ ln -s foo subdir/broken
$ chmod a-w subdir/
$ python3 -c 'import osbuild; osbuild.util.rmrf.rmtree("subdir")'
Since subdir is not writable, removing `subdir/broken` will fail
with `EPERM` and the `on_error` callback will try to fix it by
invoking `fixperms` on `subdir/broken` which will in `open` since
the target does not exist (broken symlink).
This is fixed by using `O_NOFOLLOW` to open so we will never open
the target. Instead `open` will fail with `ELOOP`; we ignore that
error and in fact we ignore now all errors from `open` since it
does not matter: if fixing the permissions didn't work `unlink`
will just fail (again) with `EPERM` and for symlinks it actually
doesn't matter since "on Linux the permissions of an ordinary
symbolic link are not used in an operations", see symlinks(7).
7a923efb1d