fix valgrind error in c_test caused by BlockBasedTableOptions

Summary:
It was creating BlockBasedTableOptions object in a loop without calling
destroy()

Test Plan: valgrind ./c_test --leak-check=full --show-reachable=yes

Reviewers: sdong, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22431