Try to fix CI bug. Add more log.

[small-turtle-1]

What problem does this PR solve?

CI test may crash when run insert_big_embedding test.

What is changed and how it works?

Possible situation: the file descriptor is closed when another thread write the bufferobj to spill directory.

But such situation violate the buffer_obj status. When a thread call BufferObj::Close(), it must has called BufferObj::Save(), which holds the lock and sets the buffer_obj.type_ to kPersistent. Then when bufferobj writes to spill directory, it must be called by BufferObj::Free(), which also holds the lock.
What's more, the log shows BufferObj::Save() is never called

And add extra log for CI debug.

Code changes

• Has Code change
• Has CI related scripts change

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Note for reviewer