dnf creates un-deleteable files in image with --installroot

[reidpr]

e.g.:

$ cat /tmp/Dockerfile
FROM redhat/ubi8:latest
RUN dnf install --assumeyes --installroot=/foo filesystem
$ ch-image reset
$ ch-image build /tmp
[...]
grown in 2 instructions: tmp
$ ch-image reset
error: can’t recursively delete directory reidpr.ch: var: Permission denied
trace: filesystem.py:539:rmtree, filesystem.py:833:reset, misc.py:203:reset, ch-image:323:main
$ rm -Rf $CH_IMAGE_STORAGE
rm: cannot remove '/scratch/reidpr.ch/img/tmp/foo/var': Permission denied
[... lots more errors ...]
$ ls -ld $CH_IMAGE_STORAGE/img/tmp/foo
dr-xr-xr-x 1 reidpr reidpr 132 Nov  2 15:41 /scratch/reidpr.ch/img/tmp/foo

foo/ is not writeable by me, so it can’t be deleted.

[reidpr]

Underlying reason is the same as #1767, but this corrupts the storage directory so seems more important.