Fix test data race in two FaultInjectionTest tests

Summary: Background sleeping tasks may conflict with test cleaning up. Wait for the sleeping tasks to finish before ending the test.

Test Plan: Run these tests.

Reviewers: andrewkr, yiwu

Reviewed By: yiwu

Subscribers: leveldb, andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D61827

db/fault_injection_test.cc

@@ -405,6 +405,7 @@ TEST_P(FaultInjectionTest, WriteOptionSyncTest) {
   env_->SetFilesystemActive(false);
   NoWriteTestReopenWithFault(kResetDropAndDeleteUnsynced);
   sleeping_task_low.WakeUp();
+  sleeping_task_low.WaitUntilDone();
 
   ASSERT_OK(OpenDB());
   std::string val;
@@ -489,6 +490,7 @@ TEST_P(FaultInjectionTest, ManualLogSyncTest) {
   env_->SetFilesystemActive(false);
   NoWriteTestReopenWithFault(kResetDropAndDeleteUnsynced);
   sleeping_task_low.WakeUp();
+  sleeping_task_low.WaitUntilDone();
 
   ASSERT_OK(OpenDB());
   std::string val;