Apply always tag to nova_virt_detect.yml

Running nova playbook with tag limit may lead to an error:

The conditional check 'nova_virt_type != 'ironic'' failed. The error
was: error while evaluating conditional (nova_virt_type != 'ironic'):
'nova_virt_type' is undefined\n\nThe error appears to be in
'/etc/ansible/roles/os_nova/tasks/main.yml': line 289, column 3, but
may be elsewhere in the file depending on the exact syntax problem.

It can be easily fixed by applying always tag to tasks from
nova_virt_detect.yml

Change-Id: I56aee80180804b8a3e3316cffc6fa8115513b8f1

tasks/main.yml

@@ -104,6 +104,10 @@
     - always
 
 - include_tasks: nova_virt_detect.yml
+  args:
+    apply:
+      tags:
+        - always
   when:
     - nova_virt_type is not defined
   tags: