Collect tox and testr output in functional tests

We need to collect tox and testr html output so that it's easier to see
what went wrong when things break.

Change-Id: I728ca7f7ea7f8e1aca9e80eab28fdf44de91f88c

.zuul.yaml

@@ -44,6 +44,7 @@
     parent: devstack-tox-functional-consumer
     description: |
       Base job for devstack-based functional tests
+    post-run: playbooks/devstack/post.yaml
     required-projects:
       # These jobs will DTRT when openstacksdk triggers them, but we want to
       # make sure stable branches of openstacksdk never get cloned by other

playbooks/devstack/post.yaml

@@ -0,0 +1,4 @@
+- hosts: all
+  roles:
+    - fetch-tox-output
+    - fetch-subunit-output