Upgrade ONOS to karaf version 4.2.6

Change-Id: I9d4086378ee42c65e8865bd1172107767bdc028d
diff --git a/tools/package/deb/prerm b/tools/package/deb/prerm
index f98e133..ee32a56 100755
--- a/tools/package/deb/prerm
+++ b/tools/package/deb/prerm
@@ -14,7 +14,7 @@
 
 # Clean up onos runtime directories
 #      TODO don't hardcode karaf version
-rm -rf /opt/onos/apache-karaf-4.2.5/
+rm -rf /opt/onos/apache-karaf-4.2.6/
 rm -rf /opt/onos/var/*
 rm -rf /opt/onos/config
 rm -rf /opt/onos/options