Set defaults for ansible_ssh_user

When setting permission for containers download/upload dir we're
using `ansible_ssh_user`. But if playbook is executed without
user being explicitly set `ansible_ssh_user` may be undefined.
In such situations dir ownership will default to `ansible_user_id`

Closes: #644

roles/download/tasks/main.yml

@@ -47,7 +47,7 @@
     download_delegate: "{% if download_localhost %}localhost{% else %}{{groups['kube-master'][0]}}{% endif %}"
 
 - name: Create dest directory for saved/loaded container images
-  file: path="{{local_release_dir}}/containers" state=directory recurse=yes mode=0755 owner={{ansible_ssh_user}}
+  file: path="{{local_release_dir}}/containers" state=directory recurse=yes mode=0755 owner={{ansible_ssh_user|default(ansible_user_id)}}
   when: "{{ download.enabled|bool and download.container|bool }}"
 
 # This is required for the download_localhost delegate to work smooth with CoreOS cluster nodes