Address Ansible bare variable usage

When executing this playbook with Ansible 2.1, the following
deprecation warning is issued in the output.

[DEPRECATION WARNING]: Using bare variables is deprecated.

This patch wraps those variables as Ansible 2.1 requires.

Change-Id: I54e7c0e85ce5145a3138103eb9c281c281410520

playbooks/utility-install.yml

@@ -96,7 +96,7 @@
       until: install_packages|success
       retries: 5
       delay: 2
-      with_items: utility_apt_packages | default([])
+      with_items: "{{ utility_apt_packages | default([]) }}"
       tags:
         - utility-apt-packages
     - name: Install pip packages
@@ -108,7 +108,7 @@
       until: install_packages|success
       retries: 5
       delay: 2
-      with_items: utility_pip_packages
+      with_items: "{{ utility_pip_packages }}"
       tags:
         - utility-pip-packages
     - name: Distribute private ssh key