Summary:
The TSAN version of tests could take quite long. Make the buck tests parallel to avoid timeouts.
Closes https://github.com/facebook/rocksdb/pull/3280

Differential Revision: D6581594

Pulled By: maysamyabandeh

fbshipit-source-id: 3f8476d8c69f0183e394fa8a2089dd8d4e90c90c