openqa: we want openqa_hostname as a role *default* variable

it seems variables in vars/main.yml are 'role variables' with
a high precedence, while variables in defaults/main.yml are
'role default variables' with a low precedence. This could be
made a hell of a lot clearer in the docs.

roles/openqa/worker/tasks/main.yml

@@ -30,9 +30,6 @@
 - include: nfs-client.yml
   when: openqa_hostname is defined and openqa_hostname != "localhost"
 
-- name: Debug openqa_hostname var
-  debug: var=openqa_hostname
-
 - name: openQA client config
   template: src=client.conf.j2 dest=/etc/openqa/client.conf owner=_openqa-worker group=root mode=0600
   tags: