Fix BlockFetcher ASAN error

Summary:
Some call sites of BlockFetcher create temporary ReadOptions and pass to BlockFetcher. The temporary object will be gone after BlockFetcher construction but BlockFetcher keep its reference, causing stack-use-after-scope. Fixing it.
Closes https://github.com/facebook/rocksdb/pull/3258

Differential Revision: D6547152

Pulled By: yiwu-arbug

fbshipit-source-id: 6b49e9dd46bb72307f5d8f88ea15faacff35b9bc

table/block_fetcher.h

@@ -45,7 +45,7 @@ class BlockFetcher {
   RandomAccessFileReader* file_;
   FilePrefetchBuffer* prefetch_buffer_;
   const Footer& footer_;
-  const ReadOptions& read_options_;
+  const ReadOptions read_options_;
   const BlockHandle& handle_;
   BlockContents* contents_;
   const ImmutableCFOptions& ioptions_;