Don't run functional test jobs for requirements changes

There is no need to run multinode or OVB jobs for changes on these
files, let's save some resources.

Change-Id: Ifb85d41324ac997e30535f04e291244d6d02ecc6

zuul.d/base.yaml

@@ -92,6 +92,7 @@
       - ^etc/.*$
       - ^metadata.json$
       - ^releasenotes/.*$
+      - ^requirements.txt$
       - ^test-requirements.txt$
       - ^spec/.*$
       - ^Puppetfile.*$

zuul.d/ovb-jobs.yaml

@@ -136,6 +136,7 @@
       - ^etc/.*$
       - ^metadata.json$
       - ^releasenotes/.*$
+      - ^requirements.txt$
       - ^test-requirements.txt$
       - ^spec/.*$
       - ^Puppetfile.*$