replace println to log4j

Our program needs to receive a large amount of data and run for a long
time.
We set the log level to WARN but "Storing iterator" "received single"
as such message written to the log file. (over yarn)

Author: fireflyc <fireflyc@126.com>

Closes #1372 from fireflyc/fix-replace-stdout-log and squashes the following commits:

e684140 [fireflyc] 'info' modified into the 'debug'
fa22a38 [fireflyc] replace println to log4j
[SPARK-2683] unidoc failed because org.apache.spark.util.CallSite uses Java keywords as value names

Renaming `short` to `shortForm` and `long` to `longForm`.

JIRA: https://issues.apache.org/jira/browse/SPARK-2683

Author: Yin Huai <huai@cse.ohio-state.edu>

Closes #1585 from yhuai/SPARK-2683 and squashes the following commits:

5ddb843 [Yin Huai] "short" and "long" are Java keyworks. In order to generate javadoc, renaming "short" to "shortForm" and "long" to "longForm".