Another case for skip_package_install

Package installation is attempted at the top of the
bifrost-create-dib-image role.  The same predicate can
be applied to prevent this if required.

Change-Id: I43679f9baa37343ae5f50723928a6da65ce78420

playbooks/roles/bifrost-create-dib-image/tasks/main.yml

@@ -17,6 +17,7 @@
   package:
     name: "{{ dib_host_required_packages }}"
     state: present
+  when: not skip_package_install | bool
 # If attempting to utilize a base Ubuntu image, diskimage-builder
 # is the recommended, and default path.
 - name: "Test if image is present"