Avoid using 'roles' reserved variable
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

bunchc/openstack-ansible,openstack/openstack-ansible,cfarquhar/openstack-ansible,stackforge/os-ansible-deployment,cfarquhar/openstack-ansible,stackforge/os-ansible-deployment,bunchc/openstack-ansible,openstack/openstack-ansible