Summary:
Add a couple of ticker stats for corruption retry count and successful retries. This PR also eliminates an extra read attempt when there's a checksum mismatch in a block read from the prefetch buffer.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12923
Test Plan: Update existing tests
Reviewed By: jowlyzhang
Differential Revision: D61024687
Pulled By: anand1976
fbshipit-source-id: 3a08403580ab244000e0d480b7ee0f5a03d76b06