Upgrade to Apache Karaf 4.2.8 to support Kafka log appender

This is required for CORD. Karaf 4.2.6 explicitelly prevents loading of
some of the bundles required to support shipping logs via Karaf.

Change-Id: I8ae525e6c8a04c0381c5e3bac39de1a7b85b4446
diff --git a/tools/build/envDefaults b/tools/build/envDefaults
index 3bb6a56..889a6dc 100644
--- a/tools/build/envDefaults
+++ b/tools/build/envDefaults
@@ -5,7 +5,7 @@
 # M2 repository and Karaf gold bits
 export M2_REPO=${M2_REPO:-~/.m2/repository}
-export KARAF_VERSION=4.2.6
+export KARAF_VERSION=4.2.8
 export KARAF_ZIP=${KARAF_ZIP:-~/Downloads/apache-karaf-$KARAF_VERSION.zip}
 export KARAF_TAR=${KARAF_TAR:-~/Downloads/apache-karaf-$KARAF_VERSION.tar.gz}
 export KARAF_DIST=$(basename $KARAF_ZIP .zip)