Run bootstrap-bridge with empty nodeset

We are currently using the default nodeset on the
infra-prod-bootstrap-bridge job which results in us waiting for a node
that we end up ignoring. As far as I can tell this job runs against
localhost and the add_host bridge entry. It ignores the default test
node from the nodeset.

Speed up job execution and reduce node waste by setting an empty nodeset
on the job.

Change-Id: I8c3ffda60b92a8655989579335a49423fbdd18a2

zuul.d/infra-prod.yaml

@@ -55,6 +55,8 @@
       - playbooks/roles/root-keys/
       - inventory/base/hosts.yaml
       - inventory/service/group_vars/bastion.yaml
+    nodeset:
+      nodes: []
 
 - job:
     name: infra-prod-base