Summary: db_test_util is used in multiple test files but it dont compile under ROCKSDB_LITE

Test Plan:
make check
make static_lib
OPT=-DROCKSDB_LITE make db_wal_test

Reviewers: igor, yhchiang, rven, sdong

Reviewed By: sdong

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D48579