[ci] Fail gracefuly in case of wrong path for task file

Change-Id: I942667988e2cd76a599ffb3d9773a757c6a512df

tests/ci/playbooks/roles/prepare-for-rally-task/tasks/main.yaml

@@ -198,6 +198,11 @@
     path: '{{ zuul.project.src_dir }}/{{ rally_task }}'
   register: rally_task_file_stat
 
+- name: Fail if Rally task file is missed.
+  fail:
+    msg: "'{{ rally_task }}' Rally task file is missed."
+  when: rally_task_file_stat.stat.exists != True
+
 - name: Copy task file
   become: True
   become_user: stack

tests/ci/playbooks/run-rally-tox.yaml

@@ -9,7 +9,9 @@
     rally_use_existing_users: false
     rally_existing_users_config: '{{ rally_home_dir }}/with-existing-users-config'
     rally_task_args_file: "100-percent-not-exist-file"
-    rally_task: "100-percent-not-exist-file"
+    # this task will not be launched, but we need to specify something real to
+    # pass a check at 'prepare-for-rally-task' role.
+    rally_task: "rally-jobs/simple-job.yaml"
   roles:
     - prepare-for-rally-task
     - run-rally-tox