Spark's HADOOP_CONF_DIR defaults to etc/hadoop/conf, not /etc/hadoop/conf

Line 69 of /usr/lib/spark/conf/spark-env.sh:

export HADOOP_CONF_DIR=${HADOOP_CONF_DIR}:-etc/hadoop/conf}

should be:

export HADOOP_CONF_DIR=${HADOOP_CONF_DIR}:-/etc/hadoop/conf}