Add openstack-tox-bashate job for scripts

We have had a bashate target in tox.ini for quite awhile, but we haven't
had a Zuul job run it on changes. Manual fixes have been needed from
time to time when someone has decided to run the linting on their own.

Rather than needing periodic cleanup, let's just have this job run on
any *.sh file changes.

Change-Id: I828715f30695fac1036b982b180a6fdaec03bc43
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

.zuul.yaml

@@ -44,6 +44,9 @@
               - ^data/.*$
               - ^deliverables/.*$
               - ^doc/.*$
+        - openstack-tox-bashate:
+            files:
+              - ^.*\.sh$
     experimental:
       jobs:
         - releases-check-approval