Fix TransactionTest.TwoPhaseMultiThreadTest under TSAN

Summary:
TransactionTest.TwoPhaseMultiThreadTest runs forever under TSAN and our CI builds time out
looks like the reason is that some threads keep running and other threads dont get a chance to increment the counter

Test Plan: run the test under TSAN

Reviewers: sdong, horuff

Reviewed By: horuff

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D58359

utilities/transactions/transaction_test.cc

@@ -602,11 +602,13 @@ TEST_F(TransactionTest, TwoPhaseMultiThreadTest) {
           t_wait_on_prepare.fetch_add(1);
           // wait for friends
           while (t_wait_on_prepare.load() < NUM_TXN_THREADS) {
+            env_->SleepForMicroseconds(10);
           }
         } else if (writer->ShouldWriteToMemtable()) {
           t_wait_on_commit.fetch_add(1);
           // wait for friends
           while (t_wait_on_commit.load() < NUM_TXN_THREADS) {
+            env_->SleepForMicroseconds(10);
           }
         } else {
           ASSERT_TRUE(false);