Separate options from arguments in several files

Summary

There are a couple of places in which we can prevent any error when the file starts with -. In some commands, we can sort this out by adding -- before the files, but not every command is susceptible to acce this change. For example tar is quite old and doesn't accept it.

Involved components

Files that can accept this change are:

• lib/gitlab/logger.rb#read_latest for tail command
• lib/backup/files.rb#dump for rsync command