The HDFS native client won't clear the last exception as expected so `hdfsGetLastExceptionRootCause` might return a staled root cause. This PR saves the last root cause here and verifies after hdfsExists returns a non-zero code.
The HDFS native client won't clear the last exception as expected so `hdfsGetLastExceptionRootCause` might return a staled root cause. This PR saves the last root cause here and verifies after hdfsExists returns a non-zero code.