Always run py27 test

The py27 test ensures that all specs are following a specific format.
The default py27 tests have an irrelevant-files list that ignores
running if especially only .rst files get updated. Override the
irrelevant files list so that it runs for nearly all changes,
only skip for release-notes (even if they do not exist here).

Change-Id: Iffb6345ddf490820ca7495f0e4a0e722acfba898

.zuul.yaml

@@ -3,7 +3,13 @@
       - openstack-specs-jobs
     check:
       jobs:
-        - openstack-tox-py27
+        - openstack-tox-py27:
+            # Override default list of files since the default
+            # ignores .rst files but we need to test .rst files here.
+            irrelevant-files:
+              - ^releasenotes/.*$
     gate:
       jobs:
-        - openstack-tox-py27
+        - openstack-tox-py27:
+            irrelevant-files:
+              - ^releasenotes/.*$