Very quick note for future reference. Please ignore.
Change loglevel in spark
Easy peasy, you can do it programatically in the application like:
spark.sparkContext.setLogLevel("WARN")
Change loglevel in yarn
This one took a while to find, you can just run spark-submit while previously exporting this envvar:
export YARN_ROOT_LOGGER=${YARN_ROOT_LOGGER:-WARN,RFA}
That´s all.