Comment 0 for bug 1833825

```
When using debirf 0.35 to create an Xenial image, debirf fails to pack the rootfs with the error below:

   image-builder: debirf> modules complete
   image-builder: debirf> creating debirf initrd ('nested')...
   image-builder: debirf> creating rootfs.cgz...
   image-builder: cpio:
   image-builder: Binary file (standard input) matches: Cannot stat
   image-builder: : No such file or directory
   image-builder: 35123 blocks

The "binary file matches" error comes from grep in pack_rootfs():

pack_rootfs() {
    # need to pack archive in fakechroot/chroot so that symlinks correctly
    # point within debirf root, instead of to host path

    # abort with a failure if our attempts to build the rootfs fail:
    set -o pipefail
    fakeroot_if_needed bash -c ". $DEBIRF_COMMON && FAKECHROOT_EXCLUDE_PATH=/does-not-exist debirf_exec sh -c 'find * |
 grep -v -e ^run/ | cpio --create -H newc'" | gzip -9 > "$1"
}

After further investigation, this appears to be an unexpected interaction with the ca-certificates package or files in /usr/share/ca-certificates. If the ca-certificates package is purged, then debirf successfully packs the rootfs.
```