Fixes the directory we copy the image to

[1] indicates that we need to sync the image to a different directory.

[1] http://logs.openstack.org/periodic/git.openstack.org/openstack/octavia/master/publish-openstack-octavia-amphora-image-ubuntu/3674c7b/job-output.txt.gz#_2018-03-21_06_17_35_183998

Change-Id: Iacc61b39d2b19442c00c9fcadbc64d924fa6fd7c

playbooks/image-build/post.yaml

@@ -2,7 +2,7 @@
   name: Copy image
   tasks:
     - synchronize:
-        dest: "{{ zuul.executor.log_root }}"
+        dest: "{{ zuul.executor.work_root }}/artifacts/"
         mode: pull
         src: "{{ ansible_user_dir }}/test-images"
         verify_host: true