Execute post_update_tasks in update playbook

We drop the post_update_steps_playbook, and execute post_update_tasks
as part of the update_steps_playbook. This will ensure that
post_update_tasks are executed, and they're executed in accordance
with the `serial: 1` ordering that update_steps_playbook is using. (We
want to avoid an issue similar to what we've had in bug #1776206).

Change-Id: I15a984172cd5532bc966269d8c68f27b5703733e
Closes-Bug: #1778471

common/deploy-steps.j2

@@ -590,6 +590,10 @@ outputs:
                   with_sequence: start=1 end={{deploy_steps_max-1}}
                   loop_control:
                     loop_var: step
+                - include: post_update_steps_tasks.yaml
+                  with_sequence: start=0 end={{post_update_steps_max-1}}
+                  loop_control:
+                    loop_var: step
       pre_upgrade_rolling_steps_tasks: |
 {%- for role in roles %}
             - include: {{role.name}}/pre_upgrade_rolling_tasks.yaml
@@ -748,16 +752,4 @@ outputs:
             - include: {{role.name}}/post_update_tasks.yaml
               when: tripleo_role_name == '{{role.name}}'
 {%- endfor %}
-      post_update_steps_playbook:
-        str_replace:
-          params:
-            DEPLOY_SOURCE_HOST: {get_param: deployment_source_hosts}
-            DEPLOY_TARGET_HOST: {get_param: deployment_target_hosts}
-          template: |
-            - hosts: DEPLOY_TARGET_HOST
-              tasks:
-                - include: post_update_steps_tasks.yaml
-                  with_sequence: start=0 end={{post_update_steps_max-1}}
-                  loop_control:
-                    loop_var: step
       boot_param_tasks: {get_file: ../extraconfig/pre_network/boot_param_tasks.yaml}