I used this with Amazon EC2 with 1 master and 2 slaves and Spark 1.2.1.
# Step 1. Change config file on the master node
nano /root/ephemeral-hdfs/conf/log4j.properties
# Before
hadoop.root.logger=INFO,console
# After
hadoop.root.logger=WARN,console
# Step 2. Replicate this change to slaves
~/spark-ec2/copy-dir /root/ephemeral-hdfs/conf/