Ignore errors when parsing tox output

Retrieving file comments is not an essential part of the job and
should not fail the job if something goes wrong.

Change-Id: Ide13343c6eda3a1fd0f45cb33cba35f3b048ece6

roles/tox/tasks/main.yaml

@@ -45,14 +45,18 @@
   tox_parse_output:
     tox_output: '{{ tox_output.stdout }}'
   register: file_comments
+  ignore_errors: yes
 
 - name: Return file comments to Zuul
-  when: file_comments.file_comments
+  when:
+    - file_comments
+    - file_comments.file_comments
   delegate_to: localhost
   zuul_return:
     data:
       zuul:
         file_comments: '{{ file_comments.file_comments }}'
+  ignore_errors: yes
 
 - name: Return tox status
   fail: