[SPARK-14881] [PYTHON] [SPARKR] pyspark and sparkR shell default log level...

[SPARK-14881] [PYTHON] [SPARKR] pyspark and sparkR shell default log level should match spark-shell/Scala

## What changes were proposed in this pull request?

Change default logging to WARN for pyspark shell and sparkR shell for a much cleaner environment.

## How was this patch tested?

Manually running pyspark and sparkR shell

Author: felixcheung <felixcheung_m@hotmail.com>

Closes #12648 from felixcheung/pylogging.