Return codes are not passed to the calling shell

Return codes for command like **hdfs dfs -test -d /** are not passed. The command always returns zero as a success. The same behavior appears in daemon mode.

This functionality is critical to implement this product for real workloads.

Start by tracing how commands such as `hdfs dfs -test -d /` are executed and how their return status reaches the calling shell. Reproduce the always-zero result in both normal and daemon modes, then verify that the command's actual status is returned in each mode.

Written by the indexing model from the issue text.