TACHYON-102 Change log to use slf4j.
Change LOG.debug to use SLF4J parameterized message to reduce String concat.

Remove toString on log to use parameterized logging.

Remove toString on log to use parameterized logging.

Revert style format change in core/pom.xml.
Small format fix on pom.xml file.
Fix the import ordering for org.slf4j.Logger
Merge pull request #440 from hsaputra/TACHYON-102_updatelog_slf4j

Tachyon-102 Move logging to SLF4J (with log4j as backend implementation)