Summary: Reuse db_test_util in listener_test

Test Plan:
make listener_test -j64 && ./listener_test
USE_CLANG=1 make listener_test -j64 && ./listener_test

Reviewers: yhchiang, rven, kradhakrishnan, anthony

Reviewed By: anthony

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D51939