Updating onos-package to display error when karaf-assembly fails.

Also, temporarily adding snapshot repo to karaf-assembly and filed bug to remove it.

Change-Id: I63bf472b3a918beec46e1b1002a29dfcb6cb7253
diff --git a/tools/build/onos-package b/tools/build/onos-package
index 22b1448..e54cff3 100755
--- a/tools/build/onos-package
+++ b/tools/build/onos-package
@@ -230,7 +230,9 @@
 [ -n "$M2_REPO" ] && args="-Dmaven.repo.local=$M2_REPO" || args=""
 cd $ONOS_ROOT/tools/package/karaf-assembly &&
   mvn $args clean install > $aux 2>&1 ||
-  ( echo "Failed to run karaf-assembly" && exit 1 )
+  ( cat $aux &&
+    printf "\nFailed to run karaf-assembly, which stages artifacts for offline deployments.\n" &&
+    exit 1 )
 
 # Before starting make sure the environment is clan - delete onos staging folder
 clean_stage_dir