Unit test fixes to enable use of Executor::KeepAlive<> in Futures (5/?)

Summary: This is blocking D8022229

Reviewed By: yfeldblum

Differential Revision: D8086230

fbshipit-source-id: 3d6f2c32190b405b9089c9d41378827e8cb2bb80

folly/io/async/EventBase.h

@@ -678,7 +678,7 @@ class EventBase : private boost::noncopyable,
 
   void keepAliveRelease() override {
     if (!inRunningEventBaseThread()) {
-      return add([=] { keepAliveRelease(); });
+      return add([this] { loopKeepAliveCount_--; });
     }
     loopKeepAliveCount_--;
   }