Solution:
Check if the file
/user/webhcat/hadoop-streaming.jar
exists on HDFS:su - webhcat hadoop dfs -ls /user/webhcat/hadoop-streaming.jar
If the above command fails, copy the Hadoop streaming JAR file:
su - webhcat /usr/bin/hadoop --config ${hadoopconfdir} fs -copyFromLocal /usr/share/hadoop/contrib/streaming/hadoop-streaming*.jar /user/webhcat/hadoop-streaming.jar