don't run dsvm tests on doc only changes

If the change is only docs, don't run the dsvm changes. This will save
a lot of test resources, and make doc patches much easier for everyone
to land and faster to iterate on.

Change-Id: Id0f498089dddab4cbf4b76b97ef87546544fba99

zuul/layout.yaml

@@ -611,6 +611,12 @@ jobs:
           - ^.*\.rst$
           - ^doc/.*$
           - ^etc/.*$
+      - project: ^openstack-dev/devstack$
+        branch: ^master$
+        all-files-match-any:
+          - ^.*\.rst$
+          - ^doc/.*$
+
   # Skip non-doc jobs for doc-only neutron changes.  Since
   # doc/source/conf.py is checked by neutron-(pep8|pylint), those jobs
   # should not be skipped.