add run-docker-prune command

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

@@ -11,3 +11,7 @@
 - import_tasks: "{{ role_path }}/tasks/dump_runtime_results.yml"
   tags:
     - always
+
+- import_tasks: "{{ role_path }}/tasks/run_docker_prune.yml"
+  tags:
+    - run-docker-prune

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

@@ -0,0 +1,4 @@
+---
+
+- name: Run Docker System Prune
+  command: "{{ matrix_host_command_docker }} system prune -a -f"