common: backup_autoremove: Improved script quality

roles/common/templates/backup_autoremove.sh

@@ -2,7 +2,7 @@
 
 set -euxo pipefail;
 
-backupsToKeep={{ backups_to_keep }};
+backupsToKeep={{ backups_to_keep | quote }};
 
 function onlyDatedFiles() {
   grep --perl-regexp '/\d+(-\d+)*(\.[^/]+)*$';
@@ -16,6 +16,6 @@ find {{ backups_directory | quote }} -type f |
   onlyDatedFiles |
   getDirName |
   sort --unique |
-  while read dir; do
+  while read -r dir; do
   find "$dir" -type f | onlyDatedFiles | sort --reverse | tail --lines=+$((backupsToKeep + 1)) | xargs rm --force;
 done