Extend tests for external DNS integration

- Verify records are deleted on server/fip deletion
- Verify records are created for ports on special networks
  (Use case 3 in [0])
- Verify the new subnet-dns-publish-fixed-ip extension works as designed

[0]
https://docs.openstack.org/neutron/latest/admin/config-dns-int-ext-serv.html

Depends-On: https://review.opendev.org/662409
Change-Id: Id7b799904f45ac2e3f913c6201aa33afef896af0
diff --git a/.zuul.yaml b/.zuul.yaml
index 1b82909..18e9b0f 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -78,6 +78,7 @@
         - standard-attr-tag
         - standard-attr-timestamp
         - subnet_allocation
+        - subnet-dns-publish-fixed-ip
         - subnetpool-prefix-ops
         - trunk
         - trunk-details
@@ -969,8 +970,8 @@
     parent: neutron-tempest-plugin-designate-scenario
     override-checkout: stable/stein
     vars:
-      network_api_extensions_common: *api_extensions_stein
       branch_override: stable/stein
+      network_api_extensions_common: *api_extensions_stein
 
 - job:
     name: neutron-tempest-plugin-designate-scenario-train