Change in to work dir before executing tox

We can't execute tox if we're not in the dir.

Change-Id: I8b6785a99f8a95b2fd9eaaad5c376a837c81154a

roles/fetch-tox-output/tasks/main.yaml

@@ -21,6 +21,8 @@
 
 - name: Find all environments
   command: tox -l
+  args:
+    chdir: "{{ zuul_work_dir }}"
   register: tox_environments
   when: tox_envlist is not defined or tox_envlist == 'all'