Add generate_overcloud_roles var to overcloud-deploy role

This enables use of the openstack overcloud roles generate command
to generate an overcloud_roles.yaml instead of requiring a hard-coded
one to be passed.

This will be useful to CI test the example roles in t-h-t/roles and also
provide coverage of the roles generate CLI itself.

Change-Id: I89e3cb0f83b4b14dce9a9eed735f7e5b84451bdd

roles/overcloud-deploy/README.md

@@ -32,6 +32,9 @@ A description of the settable variables for this role should go here, including
 * `overcloud_roles`: contents of custom `roles_data.yaml` (as a YAML
   structure, not a string). See `roles_data.yaml` in the
   tripleo-heat-templates repository for example contents.
+* `generate_overcloud_roles`: String specifying of roles to generate overcloud_roles.yaml
+   using the openstack overcloud roles generate command.
+   Note this takes precedence over the `overcloud_roles` variable.
 * `tripleo_config_download_log`: Sets the TripleO config-download log file path.
 * `ansible_steps_log`: Sets the TripleO Ansible steps log file path.
 * `config_download_args`: Sets the arguments to load config-download

roles/overcloud-deploy/tasks/create-scripts.yml

@@ -26,7 +26,7 @@
     dest: "{{ working_dir }}/config-download.yaml"
 
 - name: Write composable roles file
-  when: composable_roles|bool
+  when: composable_roles|bool and generate_overcloud_roles is not defined
   template:
     src: "overcloud_roles.yaml.j2"
     dest: "{{ working_dir }}/overcloud_roles.yaml"

roles/overcloud-deploy/tasks/pre-deploy.yml

@@ -206,6 +206,10 @@
       --roles-file {{ working_dir }}/overcloud_roles.yaml
   when: composable_roles|bool
 
+- name: Generate composable roles file
+  command: openstack overcloud roles generate --roles-path {{ overcloud_templates_path }}/roles -o {{ working_dir }}/overcloud_roles.yaml {{generate_overcloud_roles}}
+  when: composable_roles|bool and generate_overcloud_roles is defined
+
 - name: set composable service args fact
   set_fact:
     composable_args: >-