Backup Consistency

Freezer should provide a tool to check for backup consistency.

Problem description
===================

After restoring a backup, no check is available to know if the result is exactly the same as what was originally backed up.
In Freezer integration tests, we test features but the actually outcome of a restore is not verified.
Sometimes when a new feature is developed, it could silently break something else impacting the final restore result without throwing any kind of alert.
There is no point to backup anything if we cannot restore it properly. Freezer should have integration tests to ensure backup consistency.

Proposed change
==============

Develop an integration test with tempest to:
        - Checksum a directory
        - Backup it
        - Restore from the backup
        - Chacksum the restored directory
        - Compare original checksum to the restored checksum

Implement tests to cover most of backup/restore options available