Separate burnet logs into access log and error log

By default, cherrypy logs accesses and errors to the same place.
This makes it very difficult for someone to find error messages in the log.
So separating the log into different log files - one for accesses and other one
for errors - will simplify that.
Make logging level configurable

The logging level can be configured by the burnet configuration file or by the
--log-level parameter in the command line

Signed-off-by: Aline Manera <alinefm@br.ibm.com>
Message-id: 1372701015-7149-3-git-send-email-alinefm@linux.vnet.ibm.com