Add irrelevant-files to openstack-tox-functional*

Adds these irrelevant files to openstack-tox-functional and
openstack-tox-functional-py35, since they don't affect the
functional tests:
  - ^.*\.rst$
  - ^doc/.*$
  - ^releasenotes/.*$

Change-Id: I56b4765bb4f350cc5a5e87e781614973bfcf9316

zuul.d/jobs.yaml

@@ -335,6 +335,10 @@
       Run functional tests.
 
       Uses tox with the ``functional`` environment.
+    irrelevant-files:
+      - ^.*\.rst$
+      - ^doc/.*$
+      - ^releasenotes/.*$
     vars:
       tox_envlist: functional
 
@@ -345,6 +349,10 @@
       Run functional tests using python 3.5.
 
       Uses tox with the ``functional-py35`` environment.
+    irrelevant-files:
+      - ^.*\.rst$
+      - ^doc/.*$
+      - ^releasenotes/.*$
     vars:
       tox_envlist: functional-py35