Disable SmallestUnCommittedSeq in Valgrind run (#6035)

Summary:
SmallestUnCommittedSeq sometimes takes too long when run under Valgrind. The patch disables it when the tests are run under Valgrind.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6035

Differential Revision: D18509198

Pulled By: maysamyabandeh

fbshipit-source-id: 1191443b9fedb6b9c50d6b76f5c92371f5030230

utilities/transactions/write_prepared_transaction_test.cc

@@ -1578,6 +1578,7 @@ TEST_P(WritePreparedTransactionTest, AdvanceMaxEvictedSeqWithDuplicatesTest) {
   delete txn0;
 }
 
+#ifndef ROCKSDB_VALGRIND_RUN
 // Stress SmallestUnCommittedSeq, which reads from both prepared_txns_ and
 // delayed_prepared_, when is run concurrently with advancing max_evicted_seq,
 // which moves prepared txns from prepared_txns_ to delayed_prepared_.
@@ -1639,6 +1640,7 @@ TEST_P(WritePreparedTransactionTest, SmallestUnCommittedSeq) {
     delete txn;
   }
 }
+#endif  // ROCKSDB_VALGRIND_RUN
 
 TEST_P(SeqAdvanceConcurrentTest, SeqAdvanceConcurrentTest) {
   // Given the sequential run of txns, with this timeout we should never see a