Verify restore from backup in db_stress

[ajkr]

We already exercised backup functionality in db_stress according to the -backup_one_in flag. This PR verifies the backup can be restored/opened and sanity checks a few keys. Changes in this PR:

• Extracted existing backup-related logic to a helper function, TestBackupRestore
• Added restore logic, which targets a hidden directory named "./.restore<thread number>", similar to how backups target hidden directories named "./.backup<thread number>".
• After restore, check the existence/non-existence of a few keys.
• With this PR, backup is no longer compatible with clearing column families.
• Also included unrelated fixes to set ReadOptions::total_order_seek=true when using -compare_full_db_state_snapshot

Test Plan:

• well, it is a test, but I ran it several times and simulated failures to make sure it catches them

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[riversand963]

LGTM with a few comments. Thanks @ajkr for improving stress test.

[riversand963]

There are also build failures

[ajkr]

thanks for the fast/thorough review!

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@ajkr has updated the pull request. Re-import the pull request

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