Changed source image for Ubuntu 16.04

Change-Id: I819a6d98c034f317e132c67894f27c85fba0b47a
diff --git a/ubuntu-16.04/template.json b/ubuntu-16.04/template.json
index e88d7ee..aa80d0a 100644
--- a/ubuntu-16.04/template.json
+++ b/ubuntu-16.04/template.json
@@ -232,9 +232,9 @@
       "vm_name": "{{ user `distro` }}-{{ isotime \"200601021504\"  }}",
       "output_directory": "images/{{ user `distro` }}-qemu-{{ isotime \"200601021504\"  }}",
       "format": "qcow2",
-      "iso_checksum": "b0ae9a56442c409bb3ab11815c910499",
+      "iso_checksum": "566efef1d6f12e7d3a994c2405bdb642",
       "iso_checksum_type": "md5",
-      "iso_url": "https://cloud-images.ubuntu.com/xenial/current/xenial-server-cloudimg-amd64-disk1.img",
+      "iso_url": "https://cloud-images.ubuntu.com/releases/16.04/release-20180306/ubuntu-16.04-server-cloudimg-amd64-disk1.img",
       "disk_image": true,
       "accelerator": "kvm",
       "disk_size": "{{ user `disk_size`}}",