OPNFLWPLUG-644: Openflow Event logging using log4j

OPNFLWPLUG-644: Openflow Event logging using log4j

Main events of openflowplugin can be logged using a separate common
logger, which will be using log4j logging framework. This can be
configured as a log appender in etc/org.ops4j.pax.logging file, through
which we can redirect main openflowplugin event logs to a separate file.
This can be helpful in debugging the problems with different phases of
device connection to the SDN controller.

The log appender can be configured as below:
========================================================================
log4j2.logger.ofp.name = OfEventLog
log4j2.logger.ofp.level = DEBUG
log4j2.logger.ofp.additivity = false
log4j2.logger.ofp.appenderRef.OfEventRollingFile.ref = OfEventRollingFile

log4j2.appender.ofp.type = RollingRandomAccessFile
log4j2.appender.ofp.name = OfEventRollingFile
log4j2.appender.ofp.fileName = \${karaf.data}/events/openflow/openflow.log
log4j2.appender.ofp.filePattern = \${karaf.data}/events/openflow/openflow.log.%i
log4j2.appender.ofp.append = true
log4j2.appender.ofp.layout.type = PatternLayout
log4j2.appender.ofp.layout.pattern = %d{ISO8601} | %m%n
log4j2.appender.ofp.policies.type = Policies
log4j2.appender.ofp.policies.size.type = SizeBasedTriggeringPolicy
log4j2.appender.ofp.policies.size.size = 10MB
log4j2.appender.ofp.strategy.type = DefaultRolloverStrategy
log4j2.appender.ofp.strategy.max = 10
========================================================================

Change-Id: I5e86e58fb4fcbd8048dae4fea92f2021bfdbdd04
Signed-off-by: Somashekhar Javalagi <somashekhar.manohara.javalagi@ericsson.com>