Add nginx:latest to list of docker images

Change-Id: I81721a7a5a7e9d575c2490209b9e678424484cfd
diff --git a/group_vars/all b/group_vars/all
index 7adf249..dedd5b2 100644
--- a/group_vars/all
+++ b/group_vars/all
@@ -56,6 +56,11 @@
     dockerfile: "containers/xos/Dockerfile.corebuilder"
     pull: False
     publish: True
+  - name: "nginx:latest"
+    path: ""
+    dockerfile: ""
+    pull: True
+    publish: False
 
 build_optional_images: False