Surface certain messages at the end of playbook execution

Fixes #106 (Github Issue).

roles/matrix-common-after/tasks/dump_runtime_results.yml

@@ -0,0 +1,6 @@
+# Ansible outputs the message in the `item=` field.
+# It's unnecessary to output it again in the actual message, so we don't.
+- debug:
+    msg: ""
+  with_items: "{{ matrix_playbook_runtime_results }}"
+  when: "matrix_playbook_runtime_results is defined and matrix_playbook_runtime_results|length > 0"

roles/matrix-common-after/tasks/main.yml

@@ -7,3 +7,7 @@
   when: run_stop|bool
   tags:
     - stop
+
+- import_tasks: "{{ role_path }}/tasks/dump_runtime_results.yml"
+  tags:
+    - always