Replace all Ubuntu 16.04 with Ubuntu18.04 image

Change-Id: I86b84957145f7c1f253d3158e42e015c322788eb
diff --git a/jjb/xos-auth.yaml b/jjb/xos-auth.yaml
index 6b035f9..63a81a1 100644
--- a/jjb/xos-auth.yaml
+++ b/jjb/xos-auth.yaml
@@ -32,7 +32,7 @@
           branch: '$GERRIT_BRANCH'
           destination-dir: 'cord'
 
-    node: 'ubuntu16.04-basebuild-4c-8g'
+    node: 'ubuntu18.04-basebuild-4c-8g'
     project-type: freestyle
     concurrent: true