"bfs_client rmr /" do not remove blocks completely

"bfs_client rmr /" do not remove blocks completely. When chunkserver try to write an existing block，it will run error and exit.

Start by reproducing the `bfs_client rmr /` command and inspect the chunkserver path used when writing an existing block. Confirm which blocks remain after removal and whether the chunkserver errors on a subsequent write; done means recursive removal leaves no blocks and the write completes without exiting.

Written by the indexing model from the issue text.