Update tox-docs to follow build-sphinx better

The build-sphinx job uses compile and test bindep profiles, update tox-docs to use the same.

tox-docs used to run tools/test_setup due to inheriting from unittests,
remove that inheritance since we do not need it.

Update role bindep to have a default for zuul_work_dir. If this role is
used without unittests, zuul_work_dir is unset.

Change-Id: I5df8b9cd90bf5e4f4c84c7b4514fb9c575898e31

playbooks/tox-docs/pre.yaml

@@ -0,0 +1,5 @@
+- hosts: all
+  roles:
+    - role: bindep
+      bindep_dir: "{{ zuul_work_dir }}"
+

roles/bindep/defaults/main.yaml

@@ -1,3 +1,5 @@
 ---
 bindep_dir: "{{ zuul.project.src_dir }}"
 bindep_profile: compile test
+
+zuul_work_dir: "{{ zuul.project.src_dir }}"

zuul.yaml

@@ -97,14 +97,22 @@
 
 - job:
     name: tox-docs
-    parent: tox
+    # This is not parented to tox since we do not need
+    # the roles from its parent unittests.
     description: |
       Run documentation unit tests.
 
       Uses tox with the ``docs`` environment.
     vars:
       tox_envlist: docs
-    post-run: playbooks/tox/docs-post.yaml
+      bindep_profile: compile doc
+    run: playbooks/tox/run.yaml
+    pre-run:
+        - playbooks/tox-docs/pre.yaml
+        - playbooks/tox/pre.yaml
+    post-run:
+        - playbooks/tox/docs-post.yaml
+        - playbooks/tox/post.yaml
     success-url: html/
 
 - job: