mahout spark-itemsimilarity does not work on EMR 4.3

[Zhun Shen]

Hi,
mahout version: 0.11.0
EMR version: 4.3
spark version: 1.6.0

I try to run mahout spark-itemsimilarity on AWS EMR, but it told me that 
“MAHOUT_LOCAL is not set; adding HADOOP_CONF_DIR to classpath.
Cannot find Spark classpath. Is 'SPARK_HOME' set?”, Is it a bug for EMR or I 
use mahout spark in a wrong way ?