Fix an invalid variable name

According to [1], Ansible variable names should not include hyphens.
Kolla-Ansible fails with a wrong variable name 'barbican-api' when
deploying Barbican.

This patch fixes the issue that was recently introduced in [2].

[1] http://docs.ansible.com/ansible/playbooks_variables.html#id15
[2] 08ab3d8e73

Change-Id: Ib962e31ad93316e56130c9fc38dabfc918de17ce
Closes-Bug: #1703287

ansible/roles/barbican/tasks/config.yml

@@ -39,12 +39,12 @@
 
 - name: Checking whether barbican-api-paste.ini file exists
   vars:
-    barbican-api: "{{ barbican_services['barbican-api'] }}"
+    service: "{{ barbican_services['barbican-api'] }}"
   local_action: stat path="{{ node_custom_config }}/barbican/barbican-api-paste.ini"
   run_once: True
   register: check_barbican_api_paste_ini
   when:
-    - barbican-api.enabled | bool
+    - service.enabled | bool
 
 - name: Copying over barbican-api-paste.ini
   vars: