Avoid using 'roles' reserved variable

This patch clears up an Ansible warning that is thrown each time the
`get-ansible-role-requirements.yml` playbook runs. The playbook has
a variable called `roles`, but that's a reserved variable name.

The patch changes the variable name to `required_roles` to avoid the
warning.

Closes-Bug: 1735781
Change-Id: I91e5505408e53271155ac80e2997595ddf3b8781

tests/get-ansible-role-requirements.yml

@@ -27,7 +27,7 @@
         executable: /bin/bash
       when:
         - item.scm == "git" or item.scm is undefined
-      with_items: "{{ roles }}"
+      with_items: "{{ required_roles }}"
 
     - name: Ensure the default roles directory exists
       file:
@@ -42,7 +42,7 @@
           register: zuul_roles
           when:
             - item.scm == "git" or item.scm is undefined
-          with_items: "{{ roles }}"
+          with_items: "{{ required_roles }}"
         - name: Link the Zuul provided roles
           file:
             src: "/home/zuul/src/{{ item.item.src.split('/')[-3:] | join('/') }}"
@@ -91,7 +91,7 @@
 
   vars:
     ansible_python_interpreter: "/usr/bin/python"
-    roles: "{{ lookup('file', role_file) | from_yaml }}"
+    required_roles: "{{ lookup('file', role_file) | from_yaml }}"
     role_file: '../ansible-role-requirements.yml'
     role_path_default: '/etc/ansible/roles'
     git_clone_retries: 2