Bug:679 - eliminate the use of xtend in openflowplugin

- replaced xtend classes with pure java classes
- removed xtend dependency and plugin from pom

Change-Id: Ia0fdf0b7162b04143a5e654971536481f28c3b2a
Signed-off-by: Kamal Rameshan <kramesha@cisco.com>
Signed-off-by: Michal Rehak <mirehak@cisco.com>