Improved backup

Problem is that it raise exception if tarball is not created:

```
FileUtils.chmod(0700, "/non-exists")
Errno::ENOENT: No such file or directory - /non-exists
	from /usr/lib64/ruby/2.0.0/fileutils.rb:1326:in `chmod'
	from /usr/lib64/ruby/2.0.0/fileutils.rb:1326:in `chmod'
	from /usr/lib64/ruby/2.0.0/fileutils.rb:973:in `block in chmod'
	from /usr/lib64/ruby/2.0.0/fileutils.rb:972:in `each'
	from /usr/lib64/ruby/2.0.0/fileutils.rb:972:in `chmod'
	from (irb):3
	from /usr/bin/irb:12:in `<main>'
```