Add skip if for tempest running tempest on tempest commits

This commit adds a skipIf check for running tempest jobs on specific
tempest commits. If the proposed commit is a doc only, or a sample
config only change there is no need to run the tempest tests on the
commit.

Change-Id: I664288625727a19edcba6b19343d4dd9762f86dd

zuul/layout.yaml

@@ -581,6 +581,12 @@ jobs:
           - ^nova/tests/.*$
           - ^tools/.*$
           - ^tox.ini$
+      - project: ^openstack/tempest$
+        branch: ^master$
+        all-files-match-any:
+          - ^.*\.rst$
+          - ^doc/.*$
+          - ^etc/.*$
   # Skip non-doc jobs for doc-only neutron changes.  Since
   # doc/source/conf.py is checked by neutron-(pep8|pylint), those jobs
   # should not be skipped.