Summary:
This is to fix special logic to run tests inside FB.
Buck test is broken after moving to cpp_unittest(). Move c_test back to the previous approach.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7076

Test Plan: Watch the Sandcastle run

Reviewed By: ajkr

Differential Revision: D22370096

fbshipit-source-id: 4a464d0903f2c76ae2de3a8ad373ffc9bedec64c