devstack job: Add irrelevant-files

Do not run devstack and its siblings if only rst files, releasenotes, or
files in doc directory change.

This is the minimal set of irrelevant files shared by most projects
already.

Needed-By: Ie8504ba3d5d46f6338a228ed2d248ba6363e37ae
Change-Id: Id0095763eb91592c2fd1a913526883987df704bd

.zuul.yaml

@@ -80,6 +80,14 @@
     pre-run: playbooks/pre.yaml
     run: playbooks/devstack.yaml
     post-run: playbooks/post.yaml
+    irrelevant-files:
+      # Documentation related
+      - ^.*\.rst$
+      - ^api-ref/.*$
+      - ^doc/.*$
+      - ^releasenotes/.*$
+      # Translations
+      - ^.*/locale/.*po$
 
 - job:
     name: devstack-multinode