lib/Sbuild/ChrootUnshare.pm: use 'find -mindepth 1 -delete' instead of 'rm -rf'

Johannes Schauer Marin Rodriguesrequested to merge
bug1085646 into main

We use 'find' instead of Perl's remove_tree() because:

  • remove_tree() requires the CWD to be accessible or fails with cannot chdir to $CWD from $DIR_TO_DELETE: Permission denied, aborting.
  • CWD is not always accessible -- example: run sbuild from a directory only accessible by the current user (like a tempdir) in unshare mode
  • find from findutils also requires CWD to be accessible but it's easier to temporarily change CWD in a subprocess because there is no utility in perl core that changes CWD temporarily and cleans up after itself
  • we need to use find from findutils instead of rm in unshare mode because the root directory itself might not be removable by the unshared user so we only want to remove its subdirectories

Using find -mindepth 1 -delete instead of rm -rf avoids removing the root itself which might not be possible for the unshared user. The root directory itself gets removed afterwards by an rmdir.

Closes: #1085646

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