mkosi: Handle directories in debian/not-installed correctly

If a directory is specified without a glob pattern, we have to exclude
all files in that directory, so add a recursive glob to every directory
and enable the bash globstar feature when globbing to '**/*' matches all
files and directories beneath the given directory.

mkosi.images/build/mkosi.conf.d/debian-ubuntu/mkosi.build.chroot

@@ -111,8 +111,9 @@ if ! build; then
     if [[ -f debian/not-installed ]]; then
         pushd debian/tmp
         grep --invert-match "^#" ../not-installed |
-            xargs -I {} bash -O nullglob -c "printf '%s\n' {}" |
-            sed "/^$/d" |
+            xargs -I {} sh -c "test -d '{}' && echo '{}/**/*' || echo '{}'" |
+            xargs -I {} bash -O nullglob -O globstar -c "printf '%s\n' {}" |
+            sed --expression "/^$/d" --expression "s#//*#/#g" |
             xargs -I {} sh -c "test -f '{}' && echo '{}' || true" >>/tmp/packaged-files
         popd
     fi