zuul: create Neutron config dir for the devstack job

With [1] the devstack zuul job will try to update Neutron's
configuration, even though we don't use Neutron for Qinling at all.

This commit is a workaround to create a Neutron config dir to satisfy
devstack when the Neutron service is actually disabled.

[1] I2dcbd9bdb401860820e655d97aa3c4775af2827f

Change-Id: I6ecc7d631c7deccf7d5011ec68a08759441a0318

.zuul.yaml

@@ -12,6 +12,8 @@
       - ^doc/.*
       - ^qinling/tests/unit/.*$
       - ^releasenotes/.*$
+    pre-run: playbooks/pre.yaml
+    post-run: playbooks/post.yaml
     vars:
       devstack_services:
         # Disable unneeded services.

playbooks/post.yaml

@@ -0,0 +1,8 @@
+- hosts: all
+  tasks:
+    - name: cleanup the Neutron config dir
+      become: true
+      file:
+        path: /etc/neutron
+        state: absent
+

playbooks/pre.yaml

@@ -0,0 +1,10 @@
+- hosts: all
+  tasks:
+    - name: create Neutron config dir for devstack job
+      become: true
+      file:
+        path: /etc/neutron
+        owner: stack
+        recurse: yes
+        state: directory
+