Ansible doesn't like it when tasks are empty dicts so let's make sure
we aren't passing an empty dict in to the ansible tasks. Unfortunately
since we're validating non-heat processed yaml, the list_concats end
up being dicts to the yaml validator so we can't just ensure they are
always lists.
Change-Id: I13dcc4f3d4ea2ac4c7ab62887dfea293246f6530
Related-Bug: #1768019