Set default log4j level to remove warning messages

Log4j is not initialised, and running the application will
result in these warning messages

log4j:WARN No appenders could be found for logger (org.mortbay.log).
log4j:WARN Please initialize the log4j system properly.

This commit sets up default log4j settings. Refer to
https://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/BasicConfigurator.html