[SPARK-8218][SQL] Binary log math function update.

Some minor updates based on after merging #6725.

Author: Reynold Xin <rxin@databricks.com>

Closes #6871 from rxin/log and squashes the following commits:

ab51542 [Reynold Xin] Use JVM log
76fc8de [Reynold Xin] Fixed arg.
a7c1522 [Reynold Xin] [SPARK-8218][SQL] Binary log math function update.