gitlab-backup: remove tmp backup folder and backup.locked when script exit

When script exit, remove tmp backup folder which are not longuer needed. Keep this folder when backup is failing will contribute to fill the disk of server.
backup.locked is also removed, because we want to automatically retry gitlab-backup if previous backup failed, without human action. If the file is not removed automatically, backup is blocked until someone remove it.

contrib/gitlab-backup

@@ -391,6 +391,14 @@ fi
 UMASK=`umask`
 umask 0077    # XXX maybe not good - e.g. git-data/repositories should (?) be rwxrwx---
 
+function cleanup {
+  # Cleanup temp files when script exit
+  rm -rf "$tmpd"
+  # prevent blocking gitlab-backup
+  lockfile=`pwd`refs/backup.locked
+  rm -rf $lockfile
+}
+trap cleanup EXIT
 
 usage() {
     echo "Usage: gitlab-backup [pull (-keep) | restore (-vupok, -go) <commit-ish>]"