Sanitize block-based table index type and check prefix_extractor

Summary:
Respond to issue reported
https://www.facebook.com/groups/rocksdb.dev/permalink/651090261656158/
Change the Sanitize signature to take both DBOptions and CFOptions

Test Plan: unit test

Reviewers: sdong, yhchiang, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D25041