Ignore missing .tox/env/logs directories for copy

Some tox users, such as dib-utils "tox -e functional" tests, don't
actually install a venv but just shell out to some commands.
Unfortunately, I'm not sure how to tell the difference between
intentionally missing logs like this, and what might be an
unintentional failure.  ignore_missing will allow this to run.

Change-Id: Iaa85a8326e746604966a9c1bb4cc85f44e92299b

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

@@ -40,3 +40,6 @@
     rsync_opts:
       - "--ignore-missing-args"
   with_items: "{{ envlist }}"
+  # some tox runs may not create a virtualenv and thus have
+  # no ./tox/env directory
+  ignore_errors: yes