Make fb15k less verbose

Summary:
Now there's a whole bunch of
```
2019-09-20 11:47:38,334  [ainProcess] Flushing one chunk of 59071 elements to dataset 'lhs' of file data/FB15k/freebase_mtr100_mte100-test_partitioned/edges_0_0.tmp.h5
```

Reviewed By: adamlerer

Differential Revision: D17498074

fbshipit-source-id: f4f7b51b87d1760a9b39190272668e58c86784d8

Author: lw

torchbiggraph/graph_storages.py

@@ -283,8 +283,8 @@ def flush_buffer(self, _last: bool = False) -> None:
             assert self.buffer_offset == self.BUFFER_SIZE
         elif self.buffer_offset == 0:
             return
-        logger.info(f"Flushing one chunk of {self.buffer_offset} elements "
-                    f"to dataset {self.dataset_name!r} of file {self.hf.filename}")
+        logger.debug(f"Flushing one chunk of {self.buffer_offset} elements "
+                     f"to dataset {self.dataset_name!r} of file {self.hf.filename}")
         self.dataset.resize(self.dataset.shape[0] + self.buffer_offset, axis=0)
         self.dataset[-self.buffer_offset:] = self.buffer[:self.buffer_offset].numpy()
         self.buffer_offset = 0