Fix skipping glance check if deploy images not defined

Somewhere along the line, the default None value for deploy_kernel and
deploy_ramdisk gets converted to a string. Allow for both possibilities.

Change-Id: Ia06bff344262f82956da1d6548bae9a30fcdffd9
TrivialFix

ansible/roles/ironic-enrolment/tasks/main.yml

@@ -34,7 +34,9 @@
     - "{{ ironic_deploy_ramdisk }}"
   # ironic_deploy_kernel/ramdisk default to none. We don't need to know them
   # for enrolment to continue.
-  when: item is not none
+  when:
+    - item is not none
+    - item != ""
   register: deploy_image_ids
   changed_when: false