Upgrade ONOS to karaf version 4.2.6

Change-Id: I9d4086378ee42c65e8865bd1172107767bdc028d
diff --git a/tools/package/onos_stage.py b/tools/package/onos_stage.py
index 2d9afda..466c016 100755
--- a/tools/package/onos_stage.py
+++ b/tools/package/onos_stage.py
@@ -27,7 +27,7 @@
 
 written_files = set()
 now = time.time()
-karaf_version = "4.2.5"
+karaf_version = "4.2.6"
 karaf_system = "apache-karaf-" + karaf_version + "/system/"
 
 def addFile(tar, dest, file, file_size):