Fix py35 by pinning importlib-resources

The global tox installation on our test nodes is affected by an
upstream issue[1].  Additionally, the virtualenv created by tox
under those conditions is also affected.  To work around this,
pin the version of importlib-resources in the global tox install,
as well as in Zuul's own requirements.

[1] https://gitlab.com/python-devs/importlib_resources/issues/83

Change-Id: I31ed50185a71d867a2ad512ef9b526c5b607ed5c

.zuul.yaml

@@ -195,6 +195,7 @@
         - zuul-tox-docs
         - tox-pep8
         - tox-py35:
+            pre-run: playbooks/fix-tox.yaml
             irrelevant-files:
               - zuul/cmd/migrate.py
               - playbooks/zuul-migrate/.*
@@ -251,6 +252,7 @@
         - zuul-tox-docs
         - tox-pep8
         - tox-py35:
+            pre-run: playbooks/fix-tox.yaml
             irrelevant-files:
               - zuul/cmd/migrate.py
               - playbooks/zuul-migrate/.*

playbooks/fix-tox.yaml

@@ -0,0 +1,8 @@
+- hosts: all
+  pre_tasks:
+    - name: Fix importlib-resources
+      become: true
+      shell: |
+        pip3 install --upgrade importlib-resources==1.0.2
+      args:
+        executable: /bin/bash

requirements.txt

@@ -1,4 +1,6 @@
 pbr>=1.1.0
+# Temporary fix for https://gitlab.com/python-devs/importlib_resources/issues/83
+importlib-resources==1.0.2
 # Early virtualenv 20 had bad file location assumptions
 virtualenv!=20.0.0,!=20.0.1