Re-align packer templates with upstream

common-packer co-opted a variable that was in use in local templates and
therefore is causing verification errors when the matrix validate
happens.

Change-Id: Ia0232836ddcda114409b2fc71705c5c4e97d90a0
Signed-off-by: Andrew Grimberg <agrimberg@linuxfoundation.org>
diff --git a/packer/vars/ubuntu-16.04.json b/packer/vars/ubuntu-16.04.json
index 94b2014..b0e9132 100644
--- a/packer/vars/ubuntu-16.04.json
+++ b/packer/vars/ubuntu-16.04.json
@@ -1,7 +1,7 @@
 {
   "source_ami_filter_name": "*ubuntu*16.04*",
   "source_ami_filter_owner": "099720109477",
-  "cloud_user": "ubuntu",
+  "ssh_user": "ubuntu",
 
   "distro": "Ubuntu 16.04",
   "cloud_user_data": "provision/null_data.sh"