Upgrade ONOS to karaf version 4.2.6

Change-Id: I9d4086378ee42c65e8865bd1172107767bdc028d
diff --git a/tools/package/onos-prep-karaf b/tools/package/onos-prep-karaf
index 1fb51a3..c1986b3 100755
--- a/tools/package/onos-prep-karaf
+++ b/tools/package/onos-prep-karaf
@@ -12,7 +12,7 @@
 KARAF_PATCHES=$5
 SANDBOX=${6:-.}
 
-KARAF_VERSION="4.2.5"
+KARAF_VERSION="4.2.6"
 ONOS_SECURITY_MODE="false"
 
 PREFIX="onos-$ONOS_VERSION"