Disable ClockCache db_crashtest
Summary: Tempororily disable clock cache in db_crashtest while we investigate data race issue with clock cache.
Test Plan:
python ./tools/db_crashtest.py blackbox
Reviewers: sdong, lightmark, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D62481