Fix race condition in error_handler_fs_test (facebook#9325)

Summary:
We saw the below assertion failure in `error_handler_fs_test`:

```
db/error_handler_fs_test.cc:2471: Failure
Expected equality of these values:
  listener->new_bg_error()
    Which is: 16-byte object <00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00>
  Status::Aborted()
    Which is: 16-byte object <0A-00 00-00 60-61 00-00 00-00 00-00 00-00 00-00>
terminate called after throwing an instance of 'testing::internal::GoogleTestFailureException'
  what():  db/error_handler_fs_test.cc:2471: Failure
Expected equality of these values:
  listener->new_bg_error()
    Which is: 16-byte object <00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00>
  Status::Aborted()
    Which is: 16-byte object <0A-00 00-00 60-61 00-00 00-00 00-00 00-00 00-00>
Received signal 6 (Aborted)
```

The problem was completing `OnErrorRecoveryCompleted()` would
wake up the main thread and allow it to proceed to that assertion. But
that assertion assumes `OnErrorRecoveryEnd()` has completed since
only `OnErrorRecoveryEnd()` affects `new_bg_error()`.

The fix is just to make `OnErrorRecoveryCompleted()` not wake up the
main thread, by means of not implementing it.

Pull Request resolved: facebook#9325

Test Plan:
- ran `while TEST_TMPDIR=/dev/shm ./error_handler_fs_test ; do : ; done` for a while
- injected sleep between `OnErrorRecovery{Completed,End}()` callbacks, which guaranteed repro before this PR

Reviewed By: anand1976

Differential Revision: D33249200

Pulled By: ajkr

fbshipit-source-id: 1659ee183cd09f90d4dbd898f65103473fcf84a8

db/error_handler_fs_test.cc

@@ -90,13 +90,6 @@ class ErrorHandlerFSListener : public EventListener {
     }
   }
 
-  void OnErrorRecoveryCompleted(Status old_bg_error) override {
-    InstrumentedMutexLock l(&mutex_);
-    recovery_complete_ = true;
-    cv_.SignalAll();
-    old_bg_error.PermitUncheckedError();
-  }
-
   void OnErrorRecoveryEnd(const BackgroundErrorRecoveryInfo& info) override {
     InstrumentedMutexLock l(&mutex_);
     recovery_complete_ = true;

include/rocksdb/listener.h

@@ -706,7 +706,9 @@ class EventListener : public Customizable {
   // is recovered from read-only mode after an error. When this is called, it
   // means normal writes to the database can be issued and the user can
   // initiate any further recovery actions needed
-  virtual void OnErrorRecoveryCompleted(Status /* old_bg_error */) {}
+  virtual void OnErrorRecoveryCompleted(Status old_bg_error) {
+    old_bg_error.PermitUncheckedError();
+  }
 
   // A callback function for RocksDB which will be called once the recovery
   // attempt from a background retryable error is completed. The recovery