disable rate limiter test

Summary:
The test is not stable because it relies on disk and only runs for a
short period of time. So misisng a compaction/flush would greatly affect
the rate. I am disabling it for now. What do you guys think?

Test Plan: make

Reviewers: yhchiang, igor, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19599