[CI] Add no-tls-proxy job

Some gates run devstack like this and it follows different code
paths.
Let's ensure we don't break it now and then.

Change-Id: I6ee1bfc30bced53f6d7fb841e01714069919fd88
Reference: http://lists.openstack.org/pipermail/openstack-discuss/2020-July/015997.html
Reference: http://eavesdrop.openstack.org/meetings/qa/2021/qa.2021-05-11-14.00.log.html

.zuul.yaml

@@ -595,6 +595,17 @@
       zuul_copy_output:
         /opt/stack/async: logs
 
+- job:
+    name: devstack-no-tls-proxy
+    parent: tempest-full-py3
+    description: |
+      Tempest job with tls-proxy off.
+
+      Some gates run devstack like this and it follows different code paths.
+    vars:
+      devstack_services:
+        tls-proxy: false
+
 - job:
     name: devstack-platform-fedora-latest
     parent: tempest-full-py3
@@ -814,3 +825,7 @@
               - ^.*\.rst$
               - ^doc/.*$
         - devstack-platform-fedora-latest-virt-preview
+        - devstack-no-tls-proxy
+    periodic:
+      jobs:
+        - devstack-no-tls-proxy