Summary:
The patch adjusts the generation of values in batched ops stress tests so that the digits 0..9 are appended (instead of prepended) to the values written. This has the advantage of aligning the encoding of the "value base" into the value string across non-batched, batched, and CF consistency stress tests.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10872

Test Plan: Tested using some black box stress test runs.

Reviewed By: riversand963

Differential Revision: D40692847

Pulled By: ltamasi

fbshipit-source-id: 26bf8adff2944cbe416665f09c3bab89d80416b3