cuckoo table: return estimated size - 1

Summary:
This is to avoid cutting file prematurely and resulting file size to be
half of specified.

Test Plan: db_bench

Reviewers: sdong, yhchiang, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D23541

table/cuckoo_table_builder.cc

@@ -323,7 +323,7 @@ uint64_t CuckooTableBuilder::FileSize() const {
     expected_hash_table_size *= 2;
   }
   return (kvs_[0].first.size() + kvs_[0].second.size()) *
-    expected_hash_table_size;
+    expected_hash_table_size - 1;
 }
 
 // This method is invoked when there is no place to insert the target key.