Collapse host prep tasks

Since plays cannot be parallelized with a free-like strategy, we should
have a single play that runs all host prep tasks rather than blocks of
plays for each defined role. By switching to this method we have a
single play that handles the host prep tasks concept that can be run all
at once across a cloud.

Change-Id: I2670840c9beac06f8b8ffc6eaecc88b9119ad298

common/deploy-steps.j2

@@ -652,10 +652,9 @@ outputs:
                 - overcloud
                 - pre_deploy_steps
 {% endraw %}
-{%- for role in roles %}
 
-            - hosts: {{role.name}}
-              name: {{role.name}} Host prep steps
+            - hosts: {{primary_role_name}}:DEPLOY_TARGET_HOST
+              name: Host prep steps
               gather_facts: "{% raw %}{{ gather_facts | default(false) }}{% endraw %}"
               any_errors_fatal: yes
               vars:
@@ -670,16 +669,21 @@ outputs:
                 docker_puppet_process_count: DOCKER_PUPPET_PROCESS_COUNT
                 docker_puppet_mount_host_puppet: DOCKER_PUPPET_MOUNT_HOST_PUPPET
               tasks:
-                - name: {{role.name}} Host prep steps
-                  delegate_to: localhost
-                  run_once: true
-                  debug:
-                    msg: Use --start-at-task '{{role.name}} Host prep steps' to resume from this task
-                - import_tasks: {{role.name}}/host_prep_tasks.yaml
+{%- for role in roles %}
+                - name: {{role.name}} Host prep block
+                  when:
+                    - tripleo_role_name == '{{role.name}}'
+                  block:
+                    - name: {{role.name}} Host prep steps
+                      delegate_to: localhost
+                      run_once: true
+                      debug:
+                        msg: Use --start-at-task '{{role.name}} Host prep steps' to resume from this task
+                    - import_tasks: {{role.name}}/host_prep_tasks.yaml
+{%- endfor %}
               tags:
                 - overcloud
                 - host_prep_steps
-{%- endfor %}
 
 {%- for step in range(1,deploy_steps_max) %}