don't filter out stack traces, don't break hdfs

/usr/bin/hdfs default HADOOP_ROOT_LOGGER=INFO,console
Namenode default HADOOP_ROOT_LOGGER=INFO,RFA
both read hadoop-env.sh
So, conditionally modify the var only in Namenode context.

Change-Id: Ib6c77c0a69e81cd85346db8fbdf0d3615b7ca74e