[freeipa PR#2716][opened] [FileStore] Add support for the stacked backup

[stanislavlevin]

   URL: https://github.com/freeipa/freeipa/pull/2716
Author: stanislavlevin
 Title: #2716: [FileStore] Add support for the stacked backup
Action: opened

PR body:
"""
The current implementation doesn't ensure the order of backup/restoration. There are
use cases requiring the multiple backups of a file with same name but different content.
And for these situations, FileStore is not predictable.
    
* to ensure the order usual dict storage is replaced with OrderedDict one
* all search operations are performed in a reversed order
* add tests
* fix pylint errors
    
Fixes: https://pagure.io/freeipa/issue/7820
"""

To pull the PR as Git branch:
git remote add ghfreeipa https://github.com/freeipa/freeipa
git fetch ghfreeipa pull/2716/head:pr2716
git checkout pr2716