So basically this is a classic error of not-defining-the-main-class while trying to create an executable jar. when you do not let the jar have the knowledge of the main-class, the first argument is taken to be the main-class, and hence the error here.
So make sure that while you create the executable jar, you specify the main-class in the manifest.
OR
Use args[1] and args[2] respectively for input and output and execute the hadoop step something like following:
ruby elastic-mapreduce -j $jobflow --jar s3:/my-jar-location/myjar.jar --arg com.somecompany.MyMainClass --arg s3:/input --arg s3:/output