Only log error on missing jar to allow spark examples to jar.
update comment
Merge pull request #470 from tgravescs/fix_spark_examples_yarn

Only log error on missing jar to allow spark examples to jar.

Right now to run the spark examples on Yarn you have to use the --addJars option and put the jar in hdfs.  To make that nicer  so the user doesn't have to specify the --addJars option change it to simply log an error instead of throwing.