Add irrelevant files list to perfload job

We don't want perfload to run on docs, tox, or test changes, but
because it is based off a very basic job (to avoid weight) there was
no built in irrlevant-files list. This adds one to ensure that the
job only runs on code-related changes.

We need a slightly different list of files from the list used by
integrated gate jobs so do not use the changes made in
Iae26251cb455640fbc74dad326666d2015e7a46c .

Change-Id: I092b5ed19ef51c42a714984127e2fdc91d5c6c70

.zuul.yaml

@@ -30,5 +30,13 @@
         make performance related tests against it.
     required-projects:
         - git.openstack.org/openstack/placement
+    irrelevant-files:
+        - ^.*\.rst$
+        - ^api-ref/.*$
+        - ^doc/.*$
+        - ^releasenotes/.*$
+        - ^.git.*$
+        - ^placement/tests/.*$
+        - ^tox.ini$
     run: playbooks/perfload.yaml
     post-run: playbooks/post.yaml