Actually do the stress test on RCURefCount and make the TLRefCountTest not take 2 minutes
Actually do the stress test on RCURefCount and make the TLRefCountTest not take 2 minutes

Summary: Adjusting the iteration count significantly reduces the runtime of the `TLRefCount.Stress` test to ~5 seconds. Working with that same timeframe, we can get away with increasing the iteration count of the (now tested) `RCURefCount.Stress` test to 100k, up from it's previous 10k.

Reviewed By: markisaa

Differential Revision: D4477750

fbshipit-source-id: 6a89dbb65f460655db0cb33926cc331dc1904f1c

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