[Backport 2.2] #6460: Add option to keep Files in Rollback

[osrecio]

Add option to keep files in rollback and improve Readability and PSR of Backup Library

Description

Ask to user when launch command: bin/magento setup:rollback if he wants keep files to future rollbacks. Also I changed variable name protected with underscore to acomplish PSR and I imported all classes to use in class.

Fixed Issues (if relevant)

1. [2.1.1 CE] Rollback/Restore deletes database (--db) backup file in ${webroot}/var/backups. #6460: [2.1.1 CE] Rollback/Restore deletes database (--db) backup file in ${webroot}/var/backups.

Manual testing scenarios

1. create backup e.g: bin/magento setup:backup --media
2. rollback backup e.g: bin/magento setup:rollback -m 1508950479_filesystem_media.tgz
3. Answer y to question: Do you want to keep the backups?[y/N]
4. Check that your backup was kept in var/backups

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[osrecio]

Backport of: #11750 cc @dmanners

[osrecio]

Closing this ticket, I don't find the solution to not break B/C